[Detect Regressions] Highlight tests that have changed status in last X days

[KyleJu]

Taken from the rendering team test-triaging chat(internal link), one of the suggestions is to being able to filter or highlight tests that have changed status in last X days. Diff different runs could achieve a similar result, but need to more discoverable. This kind of falls under the same umbrella as #1433, #912, better surfacing/notifying/discovering regressions on wpt.fyi