Region Requirement for Terraform Deployment

### What would you like to be added?

In the [provisioning](https://www.eksworkshop.com/docs/introduction/setup/your-account#provisioning) section.
terraform apply --auto-approve fails if default region for the account in context does not have 3 Availability Zone to deploy the infrastructure.
User should:

- Check default region : aws configure get region
- Validate the region has min 3 AZ available
- If 3 AZ are not available modify ~aws config
- aws configure set default.region
OR
- vim ~/.aws/config update default region

### Why is this needed?

If this is not pre-configured user will experience error while TF deployment.

Open the provisioning section linked in the issue and review the existing Terraform deployment guidance. Document how to check the AWS default region, verify that it has at least three Availability Zones, and update the region with the shown AWS CLI or ~/.aws/config steps; done means users see this prerequisite before running terraform apply --auto-approve.

Written by the indexing model from the issue text.