idmocp-25: on-demand developer image

[avisiedo]

Helper script to build and push an image to the registry:

• It is configured with environment variables, making this container friendly.
  • BAPI_USERNAME: The username to access the image registry. Append it as a secret in a pipeline.
  • BAPI_PASSWORD: The password (or token) to access the image registry. Append it as a secret in a pipeline.
  • BAPI_REMOTE_IMAGE: The image tag to locate the image. It doesn't need a secret, but declare the environment variable in the pipeline.
• Append helper script for build-and-push-image.
• Append tests for the script.
• Append documentation about the usage of the script.

[frasertweedale]

I eyeballed it but haven't tested it. I'm just going to merge it, I don't see any reason to wait :)