Allow configuration of API endpoints to target AWS gov cloud

/kind feature

Describe the solution you'd like As a User, I want to change as a config the AWS endpoints that CAPA is using, so that I can use private regions of AWS like secret regions of the AWS cloud.

We want to use CAPA in a private AWS region, therefore we would like the capability to edit the endpoints that CAPA is targeting.

Anything else you would like to add:

Environment:

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