Backend: Speed improvements for quick action autocomplete endpoint
## Summary
The quick action autocomplete `commands` endpoint is very slow.
## Current Behavior
Per @vshushlin:
- The `commands` endpoint takes up to a few seconds to load
## Relevant Controllers
Per @kivikakk:
- `Projects::AutocompleteSourcesController#commands`
- `Groups::AutocompleteSourcesController#commands`
- These belong to `feature_category :team_planning` (~"group::project management")
## Parent Issue
https://gitlab.com/gitlab-org/gitlab/-/work_items/595193
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