sync: synchronize avatars from swarm members

This work follow the JamiAccount split started before. This moves
the ConnectionManager's callbacks code related to data transfer into
transfer_channel_handler and improves syncing by sending contact's
avatars (where a swarm is present) to new devices.

Note: for now, contact's avatar are managed by the client. So, this
code will only transmit avatars if the profile is found. For now,
the only path tested is the one used by jami-libclient. To be able
to fully sync all avatars, the avatar management should be moved in
the daemon with future work.

Finally, in syncHistory a test is added to validate the behavior.

Doc: https://git.jami.net/savoirfairelinux/ring-project/-/wikis/technical/3.8-Sync-profiles

GitLab: https://git.jami.net/savoirfairelinux/ring-project/-/issues/1282
Change-Id: Ic98da34aabf1be070a57dcac55bba0a00c555445