[Crunch] Jobs need code from multiple git repositories
The Arvados repository aims to provide useful general-purpose Crunch scripts like run-command. However, users often need to run these tools in conjunction with their own code, like shell scripts or Go programs. As a consequence, they usually end up copying the Arvados scripts into their own repositories. This comes with all the usual downsides of forking: their copies get stale, they have to manually pull bugfixes, etc.
Arvados should make it easier to get code from multiple repositories. There are lots of ways we could approach this, whether it's literally pulling from multiple repositories, using git infrastructure like submodules or subtrees, or something else. Deciding on an approach is part of this story.