Add `kusk validate` command

[aabedraba]

As a user I just want to run a command to check if my x-kusk policies are configured correctly, but I don't want to apply it to the cluster just yet.

Can we have a command kusk validate that uses the validation that we already run with kusk deploy?

[olensmar]

perhaps kusk validate would be better - linting is something we could support separately!?

[jasmingacic]

Validate will lint as well. But let's focus first on validation