feat(pageserver): collect aux file tombstones

[skyzh]

Problem

close #7800

This is a small change to enable the tombstone -> exclude from image layer path. Most of the pull request is unit tests.

Summary of changes

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]

3156 tests run: 3017 passed, 0 failed, 139 skipped (full report)

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Code coverage* (full report)

• functions: 31.5% (6557 of 20804 functions)
• lines: 48.5% (50696 of 104486 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
9f54d9e at 2024-05-31T19:19:50.563Z :recycle:}

[arpad-m]

approving, but let's wait for @koivunej 's review as well

[koivunej]

I am still antsy about "has_keys" being the wrong name. Think of a key range X with 50 keys deleted, 0 non-deleted. One would say "X is a key range with non-zero keys" or assert!(has_keys(X)), which is different what we have with "wrote_any_image".

Approving for timezone diff, required:

• apply suggestion feat(pageserver): collect aux file tombstones #7900 (comment)
• I really think something must be done for has_keys which seems just wrong

[skyzh]

resolved comments :)