Allow issue filter submission using mouse only

What does this MR do?

Enables you to click the "Keep typing and press enter" dropdown hint in order to trigger the search submission. Also places a space character at the end of the input to allow selecting another filter without needing the keyboard.

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

Why was this MR needed?

Prior to this, you could not submit an issue filter bar query with only the mouse.

Screenshots (if relevant)

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?

#25913 (closed) (meta issue)