[disconnected csv] - RFE - allow any environment variable to reference images

[raffaelespazzoli]

currently this action expects variable referencing images to start with a prefix referenced by: RELATED_IMAGE_ENV_PREFIX.
This approach might be hard to use for preexisting operators. Allow for additional logic:

1. provide a list of environment variables that reference images.
2. scan for environment variable values and consider those that match to an image, via regexp.
   The user should be able to activate either or all of those approaches.