s3_scrubber: add tenant-snapshot

[jcsp]

Problem

Downloading tenant data for analysis/debug with aws s3 cp works well for small tenants, but for larger tenants it is unlikely that one ends up with an index that matches layer files, due to the time taken to download.

Summary of changes

• Add a tenant-snapshot command to the scrubber, which reads timeline indices and then downloads the layers referenced in the index, even if they were deleted. The result is a snapshot of the tenant's remote storage state that should be usable when imported (neon_local: add "tenant import" #7399 ).

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]

2856 tests run: 2735 passed, 1 failed, 120 skipped (full report)

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Failures on Postgres 15

• test_sharding_split_failures[failure20]: debug

# Run all failed tests locally:
scripts/pytest -vv -n $(nproc) -k "test_sharding_split_failures[debug-pg15-failure20]"

Flaky tests (2)

Postgres 16

• test_vm_bit_clear_on_heap_lock: debug

Postgres 15

• test_gc_of_remote_layers: debug

Code coverage* (full report)

• functions: 28.1% (6551 of 23290 functions)
• lines: 46.7% (46241 of 99017 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
b2d5082 at 2024-04-29T12:25:22.232Z :recycle:}