feat(pageserver): remove aux v1 keyspace if user fully switches to v2

[skyzh]

Problem

A follow-up on #7462

If a user is switched to v2, their v1 data is no longer accessible, so we can remove them by not including the aux_file_key in the keyspace.

No need to merge it now in case we want to force switch some user back from v2, but I'd like to get an approval first so that we can merge it any time we want.

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]

3096 tests run: 2969 passed, 0 failed, 127 skipped (full report)

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Flaky tests (3)

Postgres 16

• test_secondary_background_downloads: release
• test_vm_bit_clear_on_heap_lock: debug

Postgres 14

• test_timeline_deletion_with_files_stuck_in_upload_queue: debug

Code coverage* (full report)

• functions: 31.4% (6413 of 20425 functions)
• lines: 48.0% (49321 of 102674 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
496e96c at 2024-05-21T18:31:07.443Z :recycle:}

[arpad-m]

looks good to me