pageserver: add supplementary branch usage stats

[jcsp]

Problem

Closes: https://github.com/neondatabase/neon/issues/8108

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[bot]]

2904 tests run: 2780 passed, 7 failed, 117 skipped (full report)

---

Failures on Postgres 16

• test_pageserver_metrics_removed_after_detach: release, debug

  Failures on Postgres 15

• test_pageserver_metrics_removed_after_detach: release, debug

  Failures on Postgres 14

• test_pg_regress[None]: debug

• test_pageserver_metrics_removed_after_detach: release, debug

  # Run all failed tests locally:
  scripts/pytest -vv -n $(nproc) -k "test_pg_regress[debug-pg14-None] or test_pageserver_metrics_removed_after_detach[release-pg14] or test_pageserver_metrics_removed_after_detach[debug-pg14] or test_pageserver_metrics_removed_after_detach[release-pg15] or test_pageserver_metrics_removed_after_detach[debug-pg15] or test_pageserver_metrics_removed_after_detach[release-pg16] or test_pageserver_metrics_removed_after_detach[debug-pg16]"

Test coverage report is not available

_{The comment gets automatically updated with the latest test results
4187ad85b0056a66d05c7c5fdc7767dd9115d6d0 at 2024-06-21T16:48:16.280Z :recycle:}