allow contributing RepoContainer routes
Created by: sqs
It was already possible to contribute RepoRevContainer routes (i.e., from the enterprise tree). Now it is possible to also contribute RepoContainer routes; i.e., repository routes that do not include the @rev
in the URL for pages that don't have a concept of "current revision".
This is useful for a feature I was prototyping (the new codemod UI). It is OK to wait to merge this until it is needed if you want.