feat: add codebuild PR, Release workflows and scripts

[phani-srikar]

Description of changes

Adds PR and Release workflows using AWS Codebuild service for CI/CD.
Adds scripts to use these workflows.
Contains some E2E workflow related changes that need to be tested and out of scope for this PR.

Issue #, if available

Description of how you validated changes

Tested by deploying the newly added testing and deployment stacks to my personal AWS account. Refer to this release commit that was generated after successful tag release workflow run. Refer to these PR checks that now get triggered in the Codegen repository.

Checklist

• PR description included
• yarn test passes
• Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)
• Breaking changes to existing customers are released behind a feature flag or major version update
• Changes are tested using sample applications for all relevant platforms (iOS/android/flutter/Javascript) that use the feature added/modified

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

[codecov-commenter]

Codecov Report

Merging #614 (507665c) into main (a33a960) will decrease coverage by 1.50%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main     #614      +/-   ##
==========================================
- Coverage   85.94%   84.44%   -1.50%     
==========================================
  Files         152      152              
  Lines        7490     6435    -1055     
  Branches     1957     1383     -574     
==========================================
- Hits         6437     5434    -1003     
+ Misses        960      901      -59     
- Partials       93      100       +7     

Impacted Files	Coverage Δ
...delgen-plugin/src/visitors/appsync-java-visitor.ts	93.24% <100.00%> (-1.57%)	⬇️

... and 116 files with indirect coverage changes

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