[Feature Requests] Publish a GitHub Action version of the validation

While the default location for the LZA config is Codepipeline, due the shortfalls for the AWS DevOps tool-chain some LZA customers manage their codebase outside the AWS echo system in some more mature offerings like GH, and as validation should happen also close to the code, GitHub Actions is an obvious choice for this.
While the SSM parameter resolution is a limiting factor, via OIDC should be trivial to address too.

Review how validation currently runs through CodePipeline and how SSM parameter resolution is handled. Define the GitHub Actions entry point and the OIDC-based access needed for validation outside AWS CodePipeline. Done means the validation can run from GitHub Actions and address the stated SSM resolution limitation.

Written by the indexing model from the issue text.