Handle TCP connections in a single command invocation

It'd be nice to have a single instance of pomerium-cli that could handle multiple TCP connections at a time.

For example, if you have an internal development server with services on a few different ports (database, SSH, etc.), it’d be handy to give users a single command they can run to open those ports all at once, and CTRL+C when they’re done.

pomerium-cli tcp host1.internal.example.com:22 --listen :2022 \
    host1.internal.example.com:5432 --listen :55432 \
    host2.internal.example.com:12345 --listen :12345

As a single process, theoretically it could even cache authentication across the services so the user would only need to authenticate once.

As it stands now, my options are:

• document individual commands to run for individual ports
• or, create a script that launches a few instances of pomerium-cli in the background, which will look confusing and make it harder for users to shut them all down.
• or, prepare some connections in Pomerium Desktop (I understand there's an export/import process) and guide users through importing that.