[FEATURE] Skip agent forwarding request to client if authentication check is already successful

Describe the feature:

SSH proxy tries to request agent forwarding channel from client before creating session to upstream server. It will cause ssh client to show this warning.

Since authentication is already checked in sshproxy.handleUpstreamPasswordAndKey function, we can skip this if authentication us successful.

Describe why this feature is needed:

Scope of feature:

[ ] TRASA codebase
[ ] dashboard
[x] server
[ ] mobile app
[ ] browser extension
[ ] device agent
[ ] website/docs

seknox / trasa

[FEATURE] Skip agent forwarding request to client if authentication check is already successful #272