The cache group fields defines under which cache group the run cache data will
belong. This is needed/useful for some next changes:
* Make cache correctly work for user direct runs. Since the user direct runs all
belong to the same run group (the user id) all the use direct runs will share the
same caches. To distinguish between the different caches we need to use something
in addition to the user id (the local repo uuid generated by the direct run
start command)
* Share the cache between multiple projects
87a472aaaf