ROSA: infer Availability Zones from subnets

[muraee]

trafficstars

/kind feature

Describe the solution you'd like Infer the Availability Zones from the provided subnets instead of passing it as a field through the API.

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):