chore(pageserver): concise error message for layer traversal

[skyzh]

Problem

Instead of showing the full path of layer traversal, we now only show tenant (in tracing context)+timeline+filename.

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]

2856 tests run: 2735 passed, 0 failed, 121 skipped (full report)

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Flaky tests (1)

Postgres 16

• test_vm_bit_clear_on_heap_lock: debug

Code coverage* (full report)

• functions: 28.1% (6601 of 23486 functions)
• lines: 46.8% (46866 of 100233 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
e1a1ab7 at 2024-05-01T15:16:13.680Z :recycle:}