Investigate if we can run whole PipelineRun in a Pod

[jlpettersson]

When discussing Design doc: Task parallelism when using workspace this may be a viable option.

Feature request

Execute whole PipelineRun in a Pod. This would eliminate all problems with Kubernetes Persistent Volumes. This can "almost" be done today, by only using a single Task. But it would be good to also be able to reuse/compose tasks e.g. from the catalog and to run Tasks in parallel (steps can currently only run in a sequence). E.g. Task Results must be implemented differently.

A new limitation is that only one ServiceAccount can be used.

Use case

To avoid the problems with using Kubernetes Persistent Volumes for sharing files between Tasks

Related to

#3052

[jlpettersson]

Closing this in favor of the linked TEP