[REQUEST] Add a Validate Command

[zprobst]

Is your feature request related to a problem? Please describe.
Add a command that validates that the annotations are valid (cron is a valid cron)

Describe the solution you'd like
See above.

Describe alternatives you've considered
We can validate out of band, but it seems that this the right place to check if annotations are set correctly. Ideally it is able to fail a CI build by exiting non-zero if something is wrong.

Additional context
N/A