Use Timeline::create_image_layer_for_rel_blocks in tiered compaction

[arpad-m]

Reduces duplication between tiered and legacy compaction by using the Timeline::create_image_layer_for_rel_blocks function. This way, we also use vectored get in tiered compaction, so the change has two benefits in one.

fixes #7659

[github-actions]

3108 tests run: 2981 passed, 0 failed, 127 skipped (full report)

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Flaky tests (1)

Postgres 14

• test_synthetic_size_while_deleting: debug

Code coverage* (full report)

• functions: 31.4% (6451 of 20545 functions)
• lines: 48.3% (49881 of 103268 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
ddb6f02 at 2024-05-23T15:19:04.314Z :recycle:}