Support for af-south-1 and sa-east-1 regions

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**Tell us about your request**
We run a globally distributed service on AWS AppRunner to serve clients around the world with favorable latency. This works well for clients in North America, Europe and Asia.
But South Africa and South America are both blank spots at the moment, and customers from those regions experience latency that is too high.

**Describe alternatives you've considered**
We could deploy EC2 instances in those regions, but AppRunner with its auto-scaling, automatic configuration and zero-downtime deployment hits a sweet spot for us, and we'd hate to have an alternative deployment model for these regions.

**Additional context**

**Attachments**