ROSA: basic docs

[enxebre]

/kind feature

Describe the solution you'd like
This introduces a common ground for collaboration on ROSA CAPA and basic ability to spin up a new cluster.

As a follow up we want to provide basic docs to spin up, delete a cluster and current limitations.

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

• Cluster-api-provider-aws version:
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):

[Skarlso]

/triage accepted