Feature: Adds AWS Cognito OIDC Support

[ben-of-codecraft]

This Implements an additional method for AWS OIDC that allows a project to leverage AWS Cognito Identity Pool to chain to AWS for deployments.

The reason for this extra step is well documented on this site:
https://catnekaise.github.io/

As it stands today, the exchange of identity between GitHub Actions and AWS IAM only allows aud and sub claims to be passed. If you want to lock down deployments more using other claims in the Github JWT it is not possible. By using a cognito identity custom mapping claims to attributes becomes possible allowing more secure limitations on Github Action assumed roles.

A walkthrough on how to set up a cognito identity pool with github action tokens as a provider can be found at https://catnekaise.github.io/github-actions-abac-aws/setup-using-aws-console/

Once the identity pool is set up and custom mapping performed you can then restricted Trust Policies by GitHub claims via PrincipalTags.

To use this, it requires new configuration options to be added to the digger.yml see below:

  - name: "my-secure-digger-project"
    dir: "prod"
    workflow: default
    workflow_file: digger_workflow.yml
    aws_role_to_assume:
      aws_role_region: "us-west-2"
      command: "arn:aws:iam::00000000000:role/github-action-deployment-role"
    aws_cognito_oidc:
      cognito_identity_pool_id: "us-east-1:00000000-0000-0000-0000-000000000000"
      aws_region: "us-east-1"
      aws_account_id: "000000000000"