cr-buildbucket.cfg and luci-scheduler.cfg files are suffering from duplication inside each file and across the files. In particular, builder names are duplicated. In general, Buildbucket had to come up with "builder mixins" to mitigate repetition. There are other configs that also have builders: cq.cfg, and json files in
https://chromium.googlesource.com/chromium/src/+/a052727f16ac1becbd68deeb2fe5e4bb3c552b5b/testing/buildbot/chromium.mac.json
We need a higher-level config for LUCI services, where a client can define a builder once and specify all of its properties including scheduling and properties. New config format must encapsulation LUCI implementation details, such as the fact that buildbucket and luci-scheduler happen to be separate services.
