Improve account picker UI

[philnagel]

Is your feature request related to a problem? Please describe.
We are a consultant working with many clients, therefore we have a large number of AGOL accounts connected to Assistant. It becomes pretty cumbersome to find the account you want to work with since they don't appear to be sorted in any meaningful way and there is no search.

Describe the solution you'd like
The easiest solution might be to make the account list sorted by username or org name / portal URL. Even better would be a search box.