pageserver: switch to jemalloc

[jcsp]

Problem

• Resident memory on long running pageserver processes tends to climb: memory fragmentation is suspected.
• Total resident memory may be a limiting factor for running on smaller nodes.

Summary of changes

• As a low-energy experiment, switch the pageserver to use jemalloc (not a net-new dependency, proxy already use it)
• Decide at end of week whether to revert before next release.

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]

3042 tests run: 2927 passed, 0 failed, 115 skipped (full report)

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Flaky tests (1)

Postgres 15

• test_statvfs_pressure_usage: debug

Code coverage* (full report)

• functions: 32.6% (6937 of 21279 functions)
• lines: 50.0% (54538 of 109034 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
8b07cfe at 2024-07-08T12:35:05.159Z :recycle:}