[FEATURE REQUEST] Add vault_ssh modules

[lkubb]

Is your feature request related to a problem? Please describe.
Vault can act as an SSH CA or create short-lived credentials on demand (using an agent). This extension should support managing associated entities and requesting certificates/credentials.

Describe the solution you'd like
Add vault_ssh modules.

Describe alternatives you've considered
None.

Additional context
They already exist in a functional form, just need to write proper tests.