GitHub support for the -pipelines and -bootstrap repositories

This is a proposal for new feature/feature enhancement: supporting GitHub for the -pipelines and -bootstrap repositories.

Customers with codebase in GitHub now have to setup the pipelines and boostrap repos in codecommit, and this means usually setting up a new set of access control policies to allow access to new repositories.

Would be great if ADF could natively integrate with GitHub repos, so to simplify customer architectures.

No files, tests, or entry points are named. Start by tracing how ADF currently configures the CodeCommit pipelines and bootstrap repositories, then determine the required GitHub integration and access controls. Done means both repository types are supported natively with simpler customer permissions.

Written by the indexing model from the issue text.