fast_import.rs: log number of jobs for pg_dump/pg_restore (neondatabase#12068)

## Problem

I have a hypothesis that import might be using lower number of jobs than
max for the VM, where the job is running. This change will help finding
this out from logs

## Summary of changes

Added logging of number of jobs, which is passed into both `pg_dump` and
`pg_restore`

Author: NanoBjorn

compute_tools/src/bin/fast_import.rs

@@ -339,6 +339,8 @@ async fn run_dump_restore(
     destination_connstring: String,
 ) -> Result<(), anyhow::Error> {
     let dumpdir = workdir.join("dumpdir");
+    let num_jobs = num_cpus::get().to_string();
+    info!("using {num_jobs} jobs for dump/restore");
 
     let common_args = [
         // schema mapping (prob suffices to specify them on one side)
@@ -354,7 +356,7 @@ async fn run_dump_restore(
         "directory".to_string(),
         // concurrency
         "--jobs".to_string(),
-        num_cpus::get().to_string(),
+        num_jobs,
         // progress updates
         "--verbose".to_string(),
     ];