USER STORY:
As a pipelines user, I would be able to choose the service account which will run the pipeline each time I run it without editing the YAML each time.

DESCRIPTION:

The UI doesn't allows the users to choose which is the service account which will run a pipeline when creating a pipeline run, so if a differetn service account must be used (for any reason), the pipeline run must be created using the YAML editor and not the nice UI we have.