[web] Call baseSetUserAvatar from onImageSelected

Summary:
Once image is successfully uploaded, we make call to baseSetUserAvatar from EditUserAvatarContext.

As of this diff, users can set emoji, image, ENS avatars (and remove them). What's missing is ImageAvatarSelectionModal to handle cropping + some error handling. Those will be handled after the thread avatar work.

Depends on D8725

Test Plan:
Works as expected:

Reviewers: ashoat, ginsu

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8726