Feature Request: Support Path to Registry Auth file #417
Description
The CNB Platform spec appears to be ambiguous with respect to where a registry auth credentials file should be placed:
If CNB_REGISTRY_AUTH is unset and a docker config.json file is present, the lifecycle SHOULD use the contents of this file to authenticate with any matching registry. The lifecycle SHOULD adhere to established docker conventions when checking for the existence of or interpreting the contents of a config.json file.
For those implementing the CNB Platform spec in Cloud Native CI/CD systems (Tekton, Argo Workflows), using a fixed absolute path for registry authentication simplifies pipeline maintenance. Adding a new environment variable to the spec (CNB_REGISTRY_AUTH_FILE) or providing CLI flag options to said auth file will help platform implementations point CNB to the right location on these systems.