2051180 - Track which pushes are actually backfilled

Status: NEW

(Tree Management :: Perfherder, task)

Description

[Myeongjun Go]

Treeherder currently triggers backfills, but it does not explicitly track which pushes were actually backfilled.
We should add a way to record the actual pushes that were backfilled when a backfill is triggered. This would give us a reliable source of truth instead of relying only on the full push range.
This feature can be used by Sherlock to check only the pushes that were actually backfilled. It could also be extended to support manually triggered backfills in the future.

In the Bk job[0] on CI, we have added backfill data to the log file like this:

BACKFILL_DATA: {"push_id":"269889","decision_task_id":"JRiy1SWdSOCILRtgs_gIOg","label":"test-linux2404-64/debug-jsreftest-3","strategy":"standard","slices":0,"push_count":1,"total_pushes":9}

Treeherder can use the Bk task id created by triggering a backfill, fetch the log for that task, and parse the BACKFILL_DATA entries to track which pushes were actually backfilled.

[0]
https://treeherder.mozilla.org/jobs?fromchange=87d71510f2cc191a4653ce41ce4bffd9d6ab21b7&selectedTaskRun=Mj7pSMRUQSSU0Fi1_KdsBw.0