test(pageserver): add test keyspace into collect_keyspace

[skyzh]

Problem

Some test cases add random keys into the timeline, but it is not part of the collect_keyspace, this will cause compaction remove the keys.

Summary of changes

The pull request adds a field to supply extra keyspaces during unit tests.

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

3234 tests run: 3092 passed, 0 failed, 142 skipped (full report)

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Flaky tests (7)

Postgres 16

• test_secondary_background_downloads: debug
• test_vm_bit_clear_on_heap_lock_blackbox: debug

Postgres 15

• test_ondemand_wal_download_in_replication_slot_funcs: release
• test_storage_controller_smoke: debug
• test_subscriber_restart: debug

Postgres 14

• test_storage_controller_smoke: debug
• test_vm_bit_clear_on_heap_lock_blackbox: release

Code coverage* (full report)

• functions: 31.6% (6631 of 20990 functions)
• lines: 48.6% (51503 of 106058 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
62d732a at 2024-06-12T17:51:40.450Z :recycle:}

[problame]

It's not clear enough from the comments why you called it extra_test_dense_keyspace as opposed to extra_test_keyspace

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What's the context for this change? AuxFilesV2 or the new compaction algorithm?

[skyzh]

collect_keyspace returns two values: dense keyspace and sparse keyspace. For sparse keyspace, the test cases can simply use AUX keys for testing; for dense keyspace, users should add their keyspace into the extra keyspace. Probably I should add both extra_dense_ks and extra_sparse_ks, but given it's not needed now, I don't plan to add both of them in this pull request.

[skyzh]

What's the context for this change? AuxFilesV2 or the new compaction algorithm?

Fixing some existing test cases that might be flaky b/c the keys could be garbage-collected, and also make the compaction algorithm tests able to use the data keyspace to do WAL replays.