Add run_id as env variable to base image.

[LennyN95]

Add an environment variable to our base image and set the MHub build-pipeline run_id at build time such that we can tie back our containers to specific builds (and all connected release and versioning information) via the run_id.

We may consider renaming run_id to build_id or mhub_build_id to prevent confusion with docker-related build IDs.