Traditional Bridge SSH connection multiplexing

[hippiehunter]

Currently, we open one SSH connection for each Traditional Bridge process on the remote server. For a very large number of processes, this is wasteful because connections are sitting idle most of the time. We can instead create up to 10 sessions per SSH connection (or more if the operating system is configured for it), which would enable us to have many more worker processes without the additional SSH overhead. This would be configurable for cases where SSH connection scaling isn’t the bottleneck.