Re-implement SSH tunnels, using `ssh` as the driver

[rolandwalker]

This issue is for voting/tracking on the re-implementation of built-in SSH tunnel functionality.

Any re-implementation should use the ssh program to establish tunnels, not the paramiko/sshtunnel libraries, which were removed in mycli 2.0.0.

There was previously some discussion and a couple of positive votes in #1464 . At the time of release 2.0.0, it is not clear that this was widely used functionality. Votes are welcome!