Remove requirement for ~group::distribution label

Summary

Removes the requirement for the groupdistribution label by instead enumerating Distribution-owned project IDs, and listing the merge requests ready for review for those projects.

Closes #1 (closed)

Testing

1. Created a new project under my account and created an MR.
2. I assigned label workflowready for review, but not groupdistribution.
3. Added my new project's ID to lib/data_sources/projects.yaml
4. Created an access token with read_api access and exported it as PRIVATE_TOKEN.
5. Ran bundle exec nanoc
6. Opened output/mrs/index.html:

Note that my demo MR Foo to bar without groupdistribution appears in the list.

You can also compare that screenshot to the following, which is the live version of the dashboard:

You can see that the dashboard generated within this MR contains all of the expected MRs collected by the live version.