Port apertis-test-cases to use the updated lava-runner

This MR is essentially composed of two parts:

1. Create a pipeline generator tool, generate-test-pipeline.py. This replaces lava-submit.py in most workflows. Instead of immediately submitting jobs to Lava, instead it creates a Gitlab pipeline file containing one Gitlab job for each Lava job. You can then have a trigger job run this pipeline, if you include it in the artifacts of your generation step.
2. Rework the structure of apertis-test-cases to match the new model, using generate-test-pipeline.py. This serves as an example both of how such reworks can be done, and also provides an initial base for consumers of apertis-test-cases to see how the parts fit together. I assume this was the justification for leaving the existing structure in place, even though submission from this repository is not actually enabled.

https://phabricator.apertis.org/T8952