Create username finding tool on the admin page

[ssemtner]

We have had cases of people forgetting their username/email that they used to make an ACM AI account. It would be helpful to have a search box on the admin portal page (src/pages/AdminPortalPage/index.tsx) that is a fuzzy search across username and email. This would let admins help recover accounts during a competition.

2 possible approaches are:

• Search only username (not email) by using the existing /v1/users api route and a client side search library like fuse.js.
• Create a new api route (admin accounts only) on the backend that includes email and username, fuzzy search on either the server or client side.