Explore ways to reduce number of SSH connections needed to connect a window using the SSH extension

[roblourens]

Need to

• Detect the platform (not doing this currently)
• Run a platform-specific install script or find an already-running remote agent
• Forward a port from the remote for the agent

[roblourens]

Added the hidden setting remote.SSH.useDynamicForwarding which will use this experimental dynamic port forwarding mode