Prevent unneeded requests to label autocomplete

What does this MR do and why?

When focusing on any Markdown field, there is no need to load labels pre-emptively. We only load labels when typing ~ or when focusing near an existing label reference.

How to set up and validate locally

There should be no change in behavior with the label autocomplete:

Screen_Recording_2023-09-08_at_10.54.00_PM

You can then verify in the Network Inspector that we don't make the labels autocomplete request unnecessarily when just focusing on the text area.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.