[web] Style and disable "Save Avatar" button when userAvatarSaveInProgress

Summary:

1. Show spinner when save avatar request is in progress.
2. Disable button when save avatar request is in progress.
3. Sneak in disable button change for CommunityCreationModal

Depends on D8278

Test Plan:
Works as expected:

Reviewers: ashoat, ginsu, rohan, inka, michal, kamil

Reviewed By: rohan

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8279