code: def create_run_group(prj):
      
      from benchbuild.utils import schema as s
  
      session = s.Session()
      experiment = prj.experiment
      group = s.RunGroup(id=prj.run_uuid, experiment=experiment.id)
      session.add(group)
      session.commit()
  
      return (group, session)
docs: Create a new 'run_group' in the database.
  
      This creates a new transaction in the database and creates a new run_group
      within this transaction. Afterwards we return both the transaction as well
      as the run_group itself. The user is responsible for committing it when the
      time comes.
  
      Args:
          prj - The project for which we open the run_group.
  
      Returns:
          A tuple (group, session) containing both the newly created run_group and
          the transaction object.