Using CodeCommit instead of GitHub

[jorgeprcn]

For the workshop's GitOps sections, we should be using CodeCommit instead of GitHub.

The way we have GitHub as part of the workshop today, specially using legacy tokens, adds to the complexity and maintainability of the workshop as a whole. Switching to CodeCommit would make the workshop more streamlined, easier to get started for customers, more secure and easier to maintain as well.

[lusoal]

Use the same model as using in this workshop: https://github.com/aws-samples/eks-saas-gitops