feat: auto-use kafka cluster after creation

[craicoverflow]

This PR adds an improvement suggested in #50

The issue with this is that the bootstrap server host is not available at this stage and so ClusterHost will be empty in the config.

Now when you create a Kafka cluster it is automatically used.

❯ rhoas kafka create --name "mykafka"                  
Creating Kafka cluster
Created Kafka cluster:
{
    "id": "1lQQ9rh4l3R5sVmGRMBnJHoo1Wv",
    "kind": "Kafka",
    "href": "/api/managed-services-api/v1/kafkas/1lQQ9rh4l3R5sVmGRMBnJHoo1Wv",
    "status": "accepted",
    "cloud_provider": "aws",
    "multi_az": true,
    "region": "us-east-1",
    "owner": "ephelan@redhat.com",
    "name": "mykafka",
    "created_at": "2020-12-09T15:11:26.251220494Z",
    "updated_at": "2020-12-09T15:11:26.251220494Z"
}

❯ rhoas kafka status                 
  ID                            NAME      STATUS    
 ----------------------------- --------- ---------- 
  1lQQ9rh4l3R5sVmGRMBnJHoo1Wv   mykafka   accepted

To achieve this, now only the Kafka Cluster ID id stored in the config, the Host and Name are fetched in real-time from the API, providing validation and ensuring the fields are up-to-date. See 3825190 (#142)

Also related: #135

[craicoverflow]

This is still a WIP, discussion around implementation considerations is ongoing in #135

[wtrocki]

Verified. This will conflict with stuff I have so let's merge it.