Make autocomplete request performant

What does this MR do?

Restricts the autocomplete_sourcesaction to returning the jsonof one specific at type at a time.

Makes sure all commands start by immediately showing the loading dropdown.

If the loading dropdown is active, we will request and load in the data for that specific at type. We manually trigger the filter again. This time, if loading dropdown is not active, initiate default filter behaviour and use the correct data template.

Also fixes an issue where setup was called multiple times by only setting up and destroying atwho on a focused/blured input.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

autocomplete_sources was requested on page load and is large.

Screenshots (if relevant)

3 requests for 3 different first-time references.

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #22802 (closed)

Closes #18435 (closed)