Generate SSH key for user

The chances of us dropping credentials right now are very low - I think if we did that, we'd need to add a way to make it easy to generate SSH keys and get them uploaded to IBM i automatically (ssh-copy-id?)

I think what we should do in the meantime, is absolutely warn the user when they log in with a password.

> You should log in using an SSH private key instead. Would you like to set one up now? [Yes] [Choose existing key]

Then the yes button could generate a key, upload it to the system, update their connection settings to point to the key, and then disconnect. What do you think of that?

Some things to consider:

* Generating an SSH key on Linux and mac is easy as chips.
* Generating an SSH key on Windows doesn't sound too easy. I believe only newer versions of Windows ship with `ssh-keygen`.
* Can `ssh2` generate a key?

No files, tests, or entry points are named. Start by tracing the extension's password-based SSH login and checking whether ssh2 supports key generation, then define the warning, platform behavior, upload, and connection-setting update as completion criteria.

Written by the indexing model from the issue text.