Don't unarchive a timeline if its ancestor is archived

[arpad-m]

If a timeline unarchival request comes in, give an error if the parent timeline is archived. This prevents us from the situation of having an archived timeline with children that are not archived.

Follow up of #8824

Part of #8088

[koivunej]

let's never log an error and then return an error.

[github-actions]

3801 tests run: 3695 passed, 0 failed, 106 skipped (full report)

---

Flaky tests (2)

Postgres 16

• test_ondemand_wal_download_in_replication_slot_funcs: release-arm64
• test_subscriber_restart: release-x86-64

Code coverage* (full report)

• functions: 32.5% (7411 of 22796 functions)
• lines: 50.7% (60194 of 118723 lines)

* collected from Rust tests only

---

_{The comment gets automatically updated with the latest test results
d2b7619 at 2024-08-29T13:08:08.286Z :recycle:}