Expose ip_version and internal delegation filters on /v1/system/ip-pools

[terror]

Resolves #9147

This PR introduces explicit filter parameters to /v1/system/ip-pools so clients can request pools by IP version and opt in to the Oxide service pools. The endpoint now accepts a new IpPoolListSelector query struct, which flows through the HTTP handler, application service, and datastore. The datastore applies the requested IP version filter and either includes or excludes the two well-known service pools that previously were always hidden.

I've also added a few integration tests that cover the new combinations, and regenerated Nexus OpenAPI documentation to include the the additional query parameters.

[bnaecker]

Thanks for taking this on @terror! This mostly looks straightforward to me, but we're also in the process of overhauling some of the internals of IP Pool management. Some of this PR could be rebased on top of those changes when they land, which are tracked by #8945. The "selector" stuff is agnostic to that for example. The internal database methods will need to change a bit.

[terror]

Thanks for taking this on @terror! This mostly looks straightforward to me, but we're also in the process of overhauling some of the internals of IP Pool management. Some of this PR could be rebased on top of those changes when they land, which are tracked by #8945. The "selector" stuff is agnostic to that for example. The internal database methods will need to change a bit.

Appreciate the heads-up! Once the IP pool overhaul lands I'll rebase and adjust the datastore related parts to fit the new shape. Let me know if there’s anything from that branch I should start factoring in now.