Create AMI on more regions
Create AMI on more regions

This commit will create AMI on 4 new regions:

- Africa (Cape Town)
- Asia Pacific (Hong Kong)
- Europe (Milan)
- Middle East (Bahrain)

Also reorder region names.

buildkite/elastic-ci-stack-for-aws,holmesjr/elastic-ci-stack-for-aws,holmesjr/elastic-ci-stack-for-aws