SH Command: add support for local port forwarding

[GGonryun]

This PR introduces support for port forwarding to our SSH command. Yargs does not expose an "example" parameter that can be used to show the optimal format for the -L argument, so instead I added a small example in the description portion of the option.

Example usage: p0 ssh <instance> -L <local_socket>:<remote_socket>

An empty -L argument such as p0 ssh <instance> -L is treated as an error. An incorrectly formatted argument returns an error:

Local port forward should be in the format `local_port:remote_port`

A separate ticket was created to support using an interactive command and port forwarding at the same time:

Currently an error message is displayed: https://linear.app/p0-security/issue/ENG-1653/p0-cli-ssh-support-executing-commands-with-port-forwarding

Invalid arguments. Specify either a command or port forwarding, not both.

A separate ticket was created to display an error if the user attempts to open a port that is not allowed locally: https://linear.app/p0-security/issue/ENG-1654/show-an-error-if-invalid-local-port-is-selected-when-port-forwarding

[linear]

ENG-1594 Support port-forwarding

Needs session document, change to AWS install and p0cli

AWS documentation: https://docs.aws.amazon.com/systems-manager/latest/userguide/session-manager-working-with-sessions-start.html#sessions-start-port-forwarding

Good resources for potential security implications:

• https://ramimac.me/ssm-iam
• https://blog.symops.com/post/jit-ec2-with-sym

[nbrahms]

Probably good as a first iteration; but I think we also need to support running a command / opening a shell AND port forwarding at the same time.