Moved CI_SSH_KEY to optional vars in docs
Moved CI_SSH_KEY to optional vars in docs

Since rsync is used by default to sync to codebase to the server, the CI_SSH_KEY is no longer a requirement since the sandbox server does not need access to the git repo to get the codebase.

docksal/bitbucket-pipelines-agent,docksal/bitbucket-pipelines-agent