We saw in production that DispatchWorker was running about twice an hour,
which would schedule twice as many jobs as it should.

For some reason, BatchWorker was running 1000 times per hour, possibly
due to Sidekiq RSS kills that caused these jobs to restart.

Adding an ExclusiveLease prevents these jobs from running more
than they should.

Relates to https://gitlab.com/gitlab-com/infrastructure/issues/4526

Signed-off-by: NRémy Coutable <remy@rymai.me>

Exports state to allow tests
Adds specs for the getters that didn't have any.

We need to preload the ancestors of search results after applying
pagination limits. This way the search results itself are paginated,
but not the ancestors.

If we don't do this, we might not preload a parent group of a search
result as it has been cut off by pagination.

This reverts merge request !19250

Refactor AutocompleteSources#label:

1. The return value was inconsistent, sometimes returning a hash and sometimes returning an ActiveModel.
2. It was inconsistent with respect to other methods in the class since they all return ActiveModels.

This allows us to check specific abilities in views, while still
enabling/disabling them at once.

added api spec

Closes #45187

We have `#allows_multiple_assignees?` defined in CE too, and `take(1)` appears
to be equivalent to `[0, 1]`.