added AVATARS_DISPLAY feature flag to all avatars render work that is ready to land. For this diff created a new hook called useShouldRenderAvatars which determines if the current user has the feature flag "on" and returns a boolean to either render or not render the avatar. The criteria for having the AVATARS_DISPLAY feature flag on is that they need to be a staff user. In subsequent diffs I will add the feature flag when introducing things like the thread avatars and user avatars in chat screen.
Depends on D7069
Linear Task: https://linear.app/comm/issue/ENG-3305/avatars-feature-flag-service