Advanced Search: Index label_ids for merge requests
Description
This adds a new Advanced search migration to add label_ids
to the merge requests.
The new label_ids
field is a keyword, intended to store an array of label ids. This is very similar to what we have done for issues !96153 (merged) without the backfilling that we will complete as part of #464302 (closed).
Related to #452399 (closed).