[keyserver][lib] Support new avatar type for encrypted images

Summary: This diff modifies lib and keyserver utilities to support new avatar upload type.

Test Plan: Flow does not fail anymore. These changes are more deeply tested with D9170 and D9624.

Reviewers: atul, ginsu

Reviewed By: atul

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9168