Header Search Refactor - Handle Errors in the component

What does this MR do and why?

Move error alert from whole page alert (createFlash) to local component only error alert (glAlert)

Screenshots or screen recordings

BEFORE:

AFTER:

How to set up and validate locally

1. Enable new header search input

   Feature.enable(:new_header_search)

2. Load page http://127.0.0.1:3000/
3. Click into header search input field
4. Type a couple of letters in the input to verify autocomplete is working as expected
5. Dissable network connection (e.g. via Chrome developer-tools)
6. Type some more letters inside header search field
7. Error alert should appear inside the dropdown

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.