Draft: [Feature flag] Remove `ci_build_finished_worker_namespace_changed`

What does this MR do?

⚠ Marked as draft because it needs to be released in a major release.

Removed the feature flag that enables and disables a namespace change for BuildFinishedWorker and ArchiveTraceWorker.

Adds a migration to rename the queue.

Issue: #335499 (closed)

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)

• I have self-reviewed this MR per code review guidelines.

• I have followed the style guides.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)