feat(pageserver): add compact queue http endpoint

[skyzh]

Problem

We cannot get the size of the compaction queue and access the info.

Part of #9114

Summary of changes

• Add an API endpoint to get the compaction queue.
• gc_compaction test case now waits until the compaction finishes.

[github-actions]

7095 tests run: 6797 passed, 0 failed, 298 skipped (full report)

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Flaky tests (5)

Postgres 15

• test_pgdata_import_smoke[None-1024-RelBlockSize.MULTIPLE_RELATION_SEGMENTS]: release-arm64
• test_pgdata_import_smoke[8-1024-RelBlockSize.MULTIPLE_RELATION_SEGMENTS]: release-arm64
• test_lr_with_slow_safekeeper: release-x86-64

Postgres 14

• test_pgdata_import_smoke[None-1024-RelBlockSize.MULTIPLE_RELATION_SEGMENTS]: release-arm64
• test_pgdata_import_smoke[8-1024-RelBlockSize.MULTIPLE_RELATION_SEGMENTS]: release-arm64

Code coverage* (full report)

• functions: 31.3% (8398 of 26865 functions)
• lines: 48.0% (66655 of 138941 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
f042def at 2024-12-18T18:02:34.340Z :recycle:}