Expiry/Reminder bugs could be improved by putting the merge date in the title, setting status-firefoxNNN flags

[chutten]

Expiry reminder bugs and emails typically look something like

Remove or update probes expiring in Firefox 112: WEBAUTHN_*

I posit they'd be catchier and more informative if they include the date that Firefox 112 starts, like

Remove or update probes expiring in Firefox 112: WEBAUTHN_* before Gecko version increases to 112 on 2023-02-13

(I'm open to improvements in the wording, but you get the idea). The merge date is present as NEXT_MERGE_DATE on product details which we already use for figuring out current and next Firefox versions.

Also, we can automatically set status flags to help sheriffs. For expiring version X, we can set status-firefox{X} to affected and status-firefox{X-1} and status-firefox{X-2} to unaffected. And for supported ESR versions Y (and, during overlap, Z) we can get Y from FIREFOX_ESR and Z from FIREFOX_ESR_NEXT from product details and set status-firefox-esr{Y} and status-firefox-esr{Z} to unaffected