client: support cmk operations

[hnousiainen]

Implement initial support for CMK operations.

[glenn-mcallister-aiven]

I have to block this, for a couple of reason:

1. Most of these commands are using optional style arguments (i.e., --cmk-id) for required arguments. That's a major UX no-no.
2. WAY MORE significantly, the current implementation is intended for BMC only, to the point where
   1. we are hiding access to the the API behind an ACL,
   2. we aren't documenting the API in our public API docs,
   3. BMC does changes only through TF, meaning they need API access only.

Once these changes get published, customers are going to see that there are "customer managed keys" commands, which is 100% what we don't want currently.