[FEATURE REQUEST] Manage SSH keys and certificates

[lkubb]

Is your feature request related to a problem? Please describe.
Managing SSH keys requires cmd.run hacks and is not stateful other than creates: /bla. There is no support for SSH certificates, which make life a lot easier and might be interesting for salt-ssh setups.

Describe the solution you'd like
Include an equivalent of the x509 modules for OpenSSH cryptography and PKI.

Describe alternatives you've considered
Keep using shell commands for keys, do not bother with certificates.

Additional context
I know that the current trend is to remove rather than add modules to Salt core, but I believe SSH auth management should be part of the core of a remote execution framework.