impr(pageserver): log image layer creation

[skyzh]

Problem

#9028 changed the image layer creation log into trace level. However, I personally find logging image layer creation useful when reading the logs -- it makes it clear that the image layer creation is happening and gives a clear idea of the progress. Therefore, I propose to continue logging them for create_image_layers set of functions.

Summary of changes

• Add info logging for all image layers created in legacy compaction.
• Add info logging for all layers creation in testing functions.

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]

4968 tests run: 4804 passed, 0 failed, 164 skipped (full report)

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Flaky tests (3)

Postgres 17

• test_sharding_split_smoke: release-x86-64
• test_scrubber_physical_gc[4]: release-x86-64

Postgres 16

• test_subscriber_restart: release-x86-64

Code coverage* (full report)

• functions: 31.8% (7418 of 23314 functions)
• lines: 49.7% (59604 of 119814 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
94ce7ec at 2024-09-18T17:04:36.634Z :recycle:}