Add option to open an SSH reverse tunnel to a remote server about serve HOT 3 OPEN

Maybe the underlying package of "Tunnel" can be used:

• https://labstack.com/docs/tunnel
• https://github.com/labstack/tunnel/blob/master/cmd/root.go

Or manually create an SSH tunnel with the stdlib, but utilize the labstack service. Their documentation contains descriptions on how to use their service with pure SSH (instead of their CLI), so if it's a public accessible service we can probably use it, too.

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Instead of having to set up your own server, the available services can be used:

• LabStack Tunnel as mentioned above
• ngrok is now v2 and closed source, but maybe the v1 client works with creating a tunnel to the v2 server?
  • https://github.com/inconshreveable/ngrok/tree/master/src/ngrok/client
• Serveo: https://serveo.net/
• localtunnel.me:
  • https://github.com/NoahShen/gotunnelme
  • https://github.com/localtunnel/go-localtunnel

Also check out:

• https://github.com/antoniomika/sish
• https://github.com/fatedier/frp

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More similar reverse tunnel tools and services are discussed here: https://news.ycombinator.com/item?id=20410552

In case that article disappears, the options were:

• https://github.com/alexellis/inlets (self-hosted, similar to https://github.com/fatedier/frp, but might be more powerful / feature-rich)
• https://github.com/CypherpunkArmory/holepunch (self-hosted as well, but seems to have a hosted version (currently only beta though))
• http://localhost.run/ (just a hosted SSH server)
• https://sshreach.me/ (seems to be closed source)
• http://www.ultrahook.com/ (only for webhooks (HTTP POST)? Closed source server, open source Ruby client)
• https://github.com/ethan2-0/onion-expose (onion service, just like what I planned in #23)

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