[FEATURE] Consider to employ ssh_auth.manage state within `ssh_auth_sources`

[mikhailmaximov]

Is your feature request related to a problem?

Current implementation of ssh_auth_sources relies on explicit use of ssh_auth_sources.absent to remove obsolete SSH public keys from .ssh/authorized_keys file.
SaltStack v3000 introduced a new state ssh_auth.manage to explicitly enumerate keys that should be in .ssh/authorized_keys file

Describe the solution you'd like

There are two possible options:

• switch ssh_auth_sources to use ssh_auth.manage state; or
• introduce a new state ssh_auth_sources.manage as less disturbing solution

Describe alternatives you've considered

This is not critical, one can use Salt's ssh_auth.manage directly

Additional context