naming of clustering commands

[jans23]

Currently the clustering commands start with the action/verb such as add-cluster-member, get-cluster-ca-certificate, and remove-cluster-member. For better clarity I suggest to start with the subject first and if possible use space instead of dash for further sepration. E.g. cluster member add, cluster ca-cert get, and cluster member remove.

This is also a general suggestion for other commands (not just clustering-related) but given the fact that clustering is still a technical preview we should get at least these commands right before a stable clustering release.

[robin-nitrokey]

If we generally want to change to command structure, I think we should do this for all commands and not only for some.

Using a space instead of a dash is not only a stylistic choice, but also turns the command into nested subcommands which has side effects e. g. regarding the --help output and auto-completion. Having a cluster subcommand makes sense to me and would only be a small change. For everything else, we should first review the effect of the structure on all commands to determine the best approach.