compute_ctl: Add more detailed tracing spans to startup subroutines

[hlinnaka]

In local dev environment, these steps take around 100 ms, and they are in the critical path of a compute startup on a compute pool hit. I don't know if it's like that in production, but as first step, add tracing spans to the functions so that they can be measured more easily.

[tristan957]

Pending Matthias' comments.

[github-actions]

7755 tests run: 7376 passed, 0 failed, 379 skipped (full report)

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Flaky tests (4)

Postgres 17

• test_change_pageserver: release-arm64-without-lfc

Postgres 16

• test_tx_abort_with_many_relations[v2]: release-x86-64-with-lfc

Postgres 15

• test_pageserver_gc_compaction_idempotent[after_restart]: release-arm64-with-lfc
• test_safekeeper_without_pageserver: release-x86-64-with-lfc

Code coverage* (full report)

• functions: 32.8% (8637 of 26357 functions)
• lines: 48.6% (73112 of 150406 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
323e237 at 2025-02-26T09:29:05.505Z :recycle:}

[hlinnaka]

also added this check_safekeepers_synced function

[hlinnaka]

Here's a screenshot from local jaeger UI with this PR and PR #10971:

The "resize_swap", "set_disk_quota", and "check_safekeepers_synced" spans are the new ones added by this PR.