[web] introduce UserProfile component

Summary:
This diff introduces the barebones user profile component. This includes the user avatar, the username, and the copy username button (but w/o the functionality). That and the other elements of the user profile will come in subsequent diffs

https://linear.app/comm/issue/ENG-4962/introduce-user-profile-component

Depends on D9408

Test Plan:
Please see screenshot below

Reviewers: atul, inka

Reviewed By: atul

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9409