Don't add the "topcrash" keyword to topcrashers in the first few hours of a release (for bugs with 1-2 total crashes)

Somehow, bugbot decided to annotate https://bugzilla.mozilla.org/show_bug.cgi?id=1748675 as a topcrash on beta (I assume specifically Firefox beta 138.0b1) here:
https://bugzilla.mozilla.org/show_bug.cgi?id=1748675#c6

...despite the fact that the bug had only 1 total crash[1] for 138.0b1 at that point, which was this one:
https://crash-stats.mozilla.org/report/index/64241243-4979-4257-8512-c85090250402

I assume this one crash qualified it as a "topcrash" because 138.0b1 had only just been released and maybe we'd only received 10-20 different crash signatures total at that point, all of which are trivially the top 10-20 crashers on beta (if only for that moment).

Rather than mistakenly adding the topcrash keyword to all such bugs on the first day of a beta release (and leaving them labeled as such until someone notices and cleans that up), maybe/probably bugbot should get some additional logic to prevent this -- maybe we need some "cooling off" period where we wait for data to come in for a new release, to be sure we've got enough data to establish useful signals, and only post if crash volume is above a certain threshold? (not sure what threshold makes sense -- it'd still be great to trip alarms if we get hundreds of crashes with a particular signature within hours of a beta going out, but maybe we don't need to rely on bugbot for that.)

[1] There's been one more crash that came in today from what looks like the same Firefox installation, https://crash-stats.mozilla.org/report/index/eeb8f728-a3ca-4714-9e75-954060250401 , but I think that was after bugbot posted its comment)

Start by tracing the bugbot path that adds the topcrash keyword, then compare its release-age and crash-volume inputs with the linked Bugzilla and crash reports. Done should prevent low-volume labels during the first hours of a release while preserving useful high-volume alerts; the cooling-off period and threshold still need a project decision.