Timeline archival test

[arpad-m]

This PR:

• Implements the rule that archived timelines require all of their children to be archived as well, as specified in the RFC. There is no fancy locking mechanism though, so the precondition can still be broken. As a TODO for later, we still allow unarchiving timelines with archived parents.
• Adds an is_archived flag to TimelineInfo
• Adds timeline_archival_config to PageserverHttpClient
• Adds a new test_timeline_archive test, loosely based on test_timeline_delete

Part of #8088

[github-actions]

3773 tests run: 3667 passed, 0 failed, 106 skipped (full report)

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Code coverage* (full report)

• functions: 32.2% (7258 of 22572 functions)
• lines: 50.3% (58795 of 116990 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
e25b59d at 2024-08-24T14:59:21.580Z :recycle:}