feat(compute): Add some basic compute_ctl metrics

[ololobus]

Problem

There are several parts of compute_ctl with a very low visibility of errors:

1. DB migrations that run async in the background after compute start.
2. Requests made to control plane (currently only GetSpec).
3. Requests made to the remote extensions server.

Summary of changes

Add new counters to quickly evaluate the amount of errors among the fleet.

Part of neondatabase/cloud#17590

[github-actions]

7403 tests run: 7052 passed, 0 failed, 351 skipped (full report)

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Flaky tests (11)

Postgres 17

• test_compute_migrations_retry: release-arm64-with-lfc, release-arm64-without-lfc
• test_pgdata_import_smoke[None-1024-RelBlockSize.MULTIPLE_RELATION_SEGMENTS]: debug-x86-64-without-lfc, release-arm64-without-lfc, release-arm64-with-lfc
• test_pgdata_import_smoke[8-1024-RelBlockSize.MULTIPLE_RELATION_SEGMENTS]: debug-x86-64-without-lfc, release-arm64-with-lfc, release-arm64-without-lfc
• test_metrics_normal_work: release-arm64-without-lfc

Postgres 15

• test_compute_migrations_retry: release-arm64-with-lfc
• test_metrics_normal_work: release-arm64-with-lfc

Code coverage* (full report)

• functions: 33.5% (8498 of 25361 functions)
• lines: 49.2% (71498 of 145197 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
67d5061 at 2025-01-27T22:55:27.600Z :recycle:}

[tristan957]

I think it could be a nice touch if the compute migration regression tests were extended to check that that the migration metric works as expected

[ololobus]

I think it could be a nice touch if the compute migration regression tests were extended to check that that the migration metric works as expected

Yeah, also had tests on the list. Added to migrations and remote extensions testing

[tristan957]

This is a good first iteration!