test(pageserver): add gc-compaction tests with delta will_init

[skyzh]

Problem

I had an impression that gc-compaction didn't test the case where the first record of the key history is will_init because of there are some code path that will panic in this case. Luckily it got fixed in #9026 so we can now implement such tests.

Part of #9114

Summary of changes

• Randomly changed some images into will_init neon wal record
• Split test_simple_bottom_most_compaction_deltas into two test cases, one of them has the bottom layer as delta layer with will_init flags, while the other is the original one with image layers.

[github-actions]

5382 tests run: 5162 passed, 0 failed, 220 skipped (full report)

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Flaky tests (1)

Postgres 15

• test_timeline_archive[4]: release-arm64

Code coverage* (full report)

• functions: 31.8% (7886 of 24832 functions)
• lines: 49.5% (62444 of 126261 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
4a5d89e at 2024-11-11T23:42:03.066Z :recycle:}