feat: skip explicit docker login and use default config if no registry credentials are provided

[tcsullens]

To support replacing ECR Login Credentials with amazon-ecr-credential-helper in our CI workflows, this customizes the Docker prepare_job Hook to skip the docker login step and "fallback" to a default docker config location if no registry credentials are provided to the Hook, i.e. the container.credentials are not provided.

Additional changes of note:

• Passing additional environment variables to the docker command to support the Credential Helper (e.g. the AWS_ vars)
• Setting the GITHUB_ACTIONS and CI environment variables to the container on creation (necessary for some of our internal logic/handling)

PR #2a of Using Docker Credential Helpers for ECR Registries in GitHub Actions

sc-135780

[tcsullens]

As mentioned in the code comment, we need these environment variables present in the shell the runner exec uses to run our hook, in order for our hook/docker to properly use the Credential Helper.

[erichmachado]

Will these be automatically filtered out from the output?

[tcsullens]

Per our discussion, added functionality in eddfa91 to ensure the values of these env vars get obfuscated if they're ever present in log output!

[tcsullens]

GitHub's Runner does this, and we depend on these being set inside the Job container, so incorporating that here on container creation (the env variables are passed to the docker command in https://github.com/wrapbook/runner-container-hooks/pull/1/files#diff-a01582fa233588888b956b55c88cb9118fb5a841a129372a3e84961890ee5b33R48-R50)