Add initial blubber pipeline.

Bug: T326731

Add a blubber file to generate a docker image containing mediawiki stream enrichment, and its runtime dependencies. These include eventutilts-python and eventutils jars.

The image is being tested locally on minikube and the new flink helm chart and operator.

Todo

• Integrate with https://gitlab.wikimedia.org/repos/releng/kokkuri for releasing via deployment-pipeline from Gitlab.
• Provide a demo Chart using this image (dedicated CR on deployment-charts). https://gerrit.wikimedia.org/r/c/operations/deployment-charts/+/880938
• Open a MR to add this repo to gitlab trusted runners: repos/releng/gitlab-trusted-runner!14 (merged)

cc / @otto @tchin @milimetric @dcausse