It is really easy to copy and paste taskgraph or mozharness configs
and cause Perfherder data to be written to the same bucket, resulting
in non-useful metrics collection.
This commit adds a taskgraph transform for the "build" kind that
attempts to look for multiple build jobs writing to the same
Perfherder bucket.
It isn't perfect. But it has already flushed out some jobs writing
to the same bucket and therefore producing bimodal Perfherder data.
MozReview-Commit-ID: COyvXwMiM32
