feat: support Ref: 'AWS::Region'

[honglu]

Description of changes:
Support Ref: 'AWS::Region'

Description of how you validated changes:
Added unit tests and end-to-end tests

Checklist:

• Write/update tests
• make pr passes

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #855 into develop will increase coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop     #855      +/-   ##
===========================================
+ Coverage    94.56%   94.57%   +<.01%     
===========================================
  Files           67       67              
  Lines         2834     2839       +5     
  Branches       508      509       +1     
===========================================
+ Hits          2680     2685       +5     
  Misses          82       82              
  Partials        72       72

Impacted Files	Coverage Δ
samtranslator/intrinsics/actions.py	98.58% <100%> (+0.05%)	⬆️

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[jlhood]

Nice. Thanks for adding this!