kubernetes: support getting kubernetes cluster details with projects command

[MorrisLaw]

Currently, we can doctl projects resources assign and doctl projects resources list the Kubernetes resource. But we can't run the doctl projects resources get do:doks:<cluster-uuid> command to get the details of the resource. We receive this error instead:

Error: "kubernetes" is an invalid resource type, consult the documentation

• This PR attempts to add the get command so that Kubernetes cluster details are returned are returned just like when we run doctl kubernetes cluster get <cluster-uuid>.

Note for reviewers: marking this as WIP for now until I can test it locally.

[MorrisLaw]

rebased

[ChiefMateStarbuck]

The get cluster function uses the list cluster API endpoint and searches for the specific cluster by id or name. These added commits address this functionality within the project test get file.