This is a master tracking bug for implementing full utilization of the LUCI domain model within CBuildbot.

So far, that seems to include:
* Move to use LUCI 'builders', one for each builder config, instead of the 3 builders that we have now (Prod, PreCQ, TryJob)

* Move to use 'buildset' tag to index builds in the same parent/child group. Also consider using newly proposed buildbucket.v2.Build.parent_id field for tracking parent/child relationships.

* Export gitiles commit metadata from all builds in a parent/child relationship such that Milo knows how to group these builds together. This will be the commit of the manifest repo from which the parent and child builds all start to build (before cherry-picking).

* Embrance 'category' fields in
https://chromium.googlesource.com/chromium/src/+/master/infra/config/global/luci-milo.cfg#318

* Export Milo blamelist metadata such that all CL's in a build are renderable by Milo (such as what Chrome has today in Milo). I'm not sure what this entails.