Search for users in store management panel

Part of #1084 (closed)

What does this MR do?

The input field for foodsaver IDs in the store management panel is replaced by a typeahead component that shows search results from the server. This allows store managers to add foodsavers by ID or name.

I tried to keep the new UserSearchInput component generic, so that we can reuse it elsewhere if necessary. It does not suggest people who are already members of the store team.

How confident are you it won't break things if deployed?

Quite sure with the search, not so sure about the frontend component

How to test

Steps a reviewer can take to verify that this MR does what it says it does e.g.

1. Checkout branch locally
2. Login as a store coordinator (storemanager1 or userstorecoordination1)
3. Go to a store for which you are responsible
4. Open the management panel above the team list
5. Search for users to add

Screenshots (if applicable)

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• use "state:" labels to track this MR's state until it was beta tested
• added an entry to CHANGELOG.md
• add a short text that can be used in the release notes
• Once your MR has been merged, you are responsible to create a testing issue in Beta Testing Repo:
  • Consider writing a detailed description in German.
  • Describe in a few sentences, what should be tested from a user perspective.
  • Also mention different settings (e.g. different browsers, roles, ...). how this change can be tested.
  • Be aware, that also non technical people should understand.

Release notes text

(A short text that will appear in the release notes and describes the change for non-technical people. Not always necessary, e.g. not for refactoring.)