InstanceTypes not available in af-south-1

## Feature Request

We were trying to create EC2 of m6i.xlarge in `af-south-1` region which was added as part of commit https://github.com/apache/libcloud/commit/e482e9e66341827cced87e156044a474306c2b4f. But it is missing the instance_types field as empty. This is not letting us to create EC2 in `af-south-1` region.

What can be the mitigation for this to do programatically?

For more information on contributing, please see https://libcloud.readthedocs.io/en/latest/development.html

Start by tracing the EC2 provider's af-south-1 region configuration and the empty instance_types field, using commit e482e9e66341827cced87e156044a474306c2b4f as context. Follow the contributing guidance in the linked development documentation. Done means the m6i.xlarge EC2 creation path works programmatically in af-south-1 and the relevant behavior is covered by an appropriate test.

Written by the indexing model from the issue text.