hold timeline open in background task using gate guard

[yliang412]

Problem

The newly added flush task in #9693 should hold timeline gate open, to avoid doing local IO after timeline shutdown completes.

Solution

Pass timeline gate guard to flush background task. The flush task do not need cancellation token b/c it will automatically shutdown when the front writer task drop the channel.

• Refactor relevant paths to pass down &Gate instead of GateGuard.

[github-actions]

6941 tests run: 6632 passed, 1 failed, 308 skipped (full report)

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Failures on Postgres 16

• test_delete_timeline_exercise_crash_safety_failpoints[Check.RETRY_WITHOUT_RESTART-timeline-delete-after-rm]: release-arm64

# Run all failed tests locally:
scripts/pytest -vv -n $(nproc) -k "test_delete_timeline_exercise_crash_safety_failpoints[release-pg16-Check.RETRY_WITHOUT_RESTART-timeline-delete-after-rm]"

Flaky tests (5)

Postgres 17

• test_deletion_queue_recovery[validate-lose]: release-arm64
• test_wal_restore_http[True]: debug-x86-64

Postgres 15

• test_cli_start_stop: release-arm64
• test_pull_timeline[True]: release-arm64

Postgres 14

• test_pull_timeline[True]: release-arm64

Test coverage report is not available

_{The comment gets automatically updated with the latest test results
f5245f1 at 2024-11-27T16:47:30.948Z :recycle:}