[keyserver] Send updateTypes.UPDATE_CURRENT_USER to currentUser on updateUserAvatar

Summary: Because we're using updatesForCurrentSession: 'return' these updates will NOT be sent for current session. This is for other sessions where the user might be logged in.

Test Plan:
Works as expected:

Reviewers: ashoat, ginsu

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D7682