feat(otlp): Derive a sentry.op attribute for V2 spans (#4796)

In support of [Span Field
Transition](https://linear.app/getsentry/document/span-field-transition-e0e4b8e59f11),
this PR adds a change to how `SpanV2` spans are converted to `Span`.
Before, we used to put the `name` field of `SpanV2` into the `op` field
of the `Span`. This is _roughly_ correct, but not quite correct.
Instead, it does this:

1. If the payload includes a `sentry.op` attribute (as it might, in new
SDKs that send `SpanV2` spans that aren't covered under OTel
definitions, like `ui.click`), we respect `sentry.op`
2. If the payload did not include a `sentry.op`, derives a simple
`sentry.op` from the available attributes
3. If it's not possible to derive `sentry.op`, sets it to `"default"`

The logic is copied from the [JavaScript
SDK](https://github.com/getsentry/sentry-javascript/blob/master/packages/opentelemetry/src/utils/parseSpanDescription.ts#L41-L94)
which already has this logic.

N.B. Once this logic is active, SDKs technically don't have to infer the
`op`, since Relay will do it.

This has two important upstream/downstream implications (but they are
negotiable)

1. `sentry.op` will never be blank, and it won't fall back to `name`.
It'll be `"default"`. This should be very rare, but that's the fallback
for missing transaction ops, so I adopted it here. Another alternative
is to fall back to `name`, but I'm trying to avoid mixing those concepts
as much as possible
2. We will rely on frontend SDKs to continue sending `sentry.op` for
cases where we can't derive it for now

The Rust code here is no good, style and logic suggestions would be very
welcome!

Author: gggritso

CHANGELOG.md

@@ -25,6 +25,7 @@
 - Set default sdk name for playstation crashes. ([#4802](https://github.com/getsentry/relay/pull/4802))
 - Skip large attachments on playstation crashes. ([#4793](https://github.com/getsentry/relay/pull/4793))
 - Use the received timestamp as observed nanos for logs. ([#4810](https://github.com/getsentry/relay/pull/4810))
+- Derive a `sentry.op` attribute for V2 spans ([#4796](https://github.com/getsentry/relay/pull/4796))
 
 ## 25.5.1
 

relay-spans/src/otel_to_sentry.rs

@@ -9,6 +9,8 @@ use relay_protocol::Error;
 /// This uses attributes in the OTEL span to populate various fields in the Sentry span.
 /// * The Sentry span's `name` field may be set based on `db` or `http` attributes
 ///   if the OTEL span's `name` is empty.
+/// * The Sentry span's `op` field will be inferred based on the OTEL span's `sentry.op` attribute,
+///   or other available attributes if `sentry.op` is not provided.
 /// * The Sentry span's `description` field may be set based on `db` or `http` attributes
 ///   if the OTEL span's `sentry.description` attribute is empty.
 /// * The Sentry span's `status` field is set based on the OTEL span's `status` field and
@@ -113,7 +115,7 @@ mod tests {
           "timestamp": 1697620454.980079,
           "start_timestamp": 1697620454.98,
           "exclusive_time": 1000.0,
-          "op": "middleware - fastify -> @fastify/multipart",
+          "op": "http",
           "span_id": "e342abb1214ca181",
           "parent_span_id": "0c7a7dea069bf5a6",
           "trace_id": "89143b0763095bd9c9955e8175d1fb23",
@@ -163,7 +165,7 @@ mod tests {
           "timestamp": 1697620454.980079,
           "start_timestamp": 1697620454.98,
           "exclusive_time": 3200.0,
-          "op": "middleware - fastify -> @fastify/multipart",
+          "op": "default",
           "span_id": "e342abb1214ca181",
           "parent_span_id": "0c7a7dea069bf5a6",
           "trace_id": "89143b0763095bd9c9955e8175d1fb23",
@@ -196,7 +198,7 @@ mod tests {
           "timestamp": 1697620454.980079,
           "start_timestamp": 1697620454.98,
           "exclusive_time": 0.0788,
-          "op": "middleware - fastify -> @fastify/multipart",
+          "op": "default",
           "span_id": "e342abb1214ca181",
           "parent_span_id": "0c7a7dea069bf5a6",
           "trace_id": "89143b0763095bd9c9955e8175d1fb23",
@@ -249,7 +251,7 @@ mod tests {
           "timestamp": 1697620454.980079,
           "start_timestamp": 1697620454.98,
           "exclusive_time": 0.0788,
-          "op": "database query",
+          "op": "default",
           "span_id": "e342abb1214ca181",
           "parent_span_id": "0c7a7dea069bf5a6",
           "trace_id": "89143b0763095bd9c9955e8175d1fb23",
@@ -312,7 +314,7 @@ mod tests {
           "timestamp": 1697620454.980079,
           "start_timestamp": 1697620454.98,
           "exclusive_time": 0.0788,
-          "op": "database query",
+          "op": "default",
           "span_id": "e342abb1214ca181",
           "parent_span_id": "0c7a7dea069bf5a6",
           "trace_id": "89143b0763095bd9c9955e8175d1fb23",
@@ -363,7 +365,7 @@ mod tests {
           "timestamp": 1697620454.980079,
           "start_timestamp": 1697620454.98,
           "exclusive_time": 0.0788,
-          "op": "http client request",
+          "op": "http.client",
           "span_id": "e342abb1214ca181",
           "parent_span_id": "0c7a7dea069bf5a6",
           "trace_id": "89143b0763095bd9c9955e8175d1fb23",
@@ -518,7 +520,7 @@ mod tests {
           "timestamp": 123.5,
           "start_timestamp": 123.0,
           "exclusive_time": 500.0,
-          "op": "myname",
+          "op": "myop",
           "span_id": "fa90fdead5f74052",
           "parent_span_id": "fa90fdead5f74051",
           "trace_id": "4c79f60c11214eb38604f4ae0781bfb2",
@@ -532,8 +534,7 @@ mod tests {
             "sentry.release": "[email protected]",
             "sentry.segment.name": "my 1st transaction",
             "sentry.sdk.name": "sentry.php",
-            "sentry.name": "myname",
-            "sentry.op": "myop"
+            "sentry.name": "myname"
           },
           "links": [],
           "platform": "php"
@@ -559,6 +560,7 @@ mod tests {
           "timestamp": 123.5,
           "start_timestamp": 123.0,
           "exclusive_time": 500.0,
+          "op": "default",
           "span_id": "e342abb1214ca181",
           "parent_span_id": "0c7a7dea069bf5a6",
           "trace_id": "89143b0763095bd9c9955e8175d1fb23",
@@ -588,6 +590,7 @@ mod tests {
           "timestamp": 123.5,
           "start_timestamp": 123.0,
           "exclusive_time": 500.0,
+          "op": "default",
           "span_id": "e342abb1214ca181",
           "parent_span_id": "0c7a7dea069bf5a6",
           "trace_id": "89143b0763095bd9c9955e8175d1fb23",
@@ -617,6 +620,7 @@ mod tests {
           "timestamp": 123.5,
           "start_timestamp": 123.0,
           "exclusive_time": 500.0,
+          "op": "default",
           "span_id": "e342abb1214ca181",
           "parent_span_id": "0c7a7dea069bf5a6",
           "trace_id": "89143b0763095bd9c9955e8175d1fb23",
@@ -676,6 +680,7 @@ mod tests {
           "timestamp": 0.0,
           "start_timestamp": 0.0,
           "exclusive_time": 0.0,
+          "op": "default",
           "span_id": "e342abb1214ca181",
           "trace_id": "3c79f60c11214eb38604f4ae0781bfb2",
           "status": "unknown",