Linux Bash rsync remote to remote with forwarding keys

We need it for loading files directly from one remote server to another one where we have SSH access.

SSH access from a Workstation -> Server1 -> rsync loading files -> Server2

ssh -v username@server1

find an identity SSH key for sure

ssh-add <the_key>

ssh -A username@server1

run with A option for allowing forwarding keys 

rsync -azP --exclude '.4y8-folder' --exclude 'file.tar.gz' pub/media/ username@server2:pub/media/