Support GitHub's `@today` in `closed` and other date-based search filters

[TylerLeonhardt]

GitHub issue search has these handy variables for date based searching:

• closed:@today
• closed:>@today-1w
• closed:>@today-1m

This appears to be resolved to a date client side and then sent over. We would probably need to resolve this syntax the same way.

This would be nice for endgame too because we could ignore issues that were closed today since they are likely not in the Insiders build.

[jrieken]

This would be nice for endgame too because we could ignore issues that were closed today since they are likely not in the Insiders build.

We have insiders-released for this which IMO is more powerful because it considers the actual commits

[TylerLeonhardt]

@jrieken true, but insiders-released is only a core concept today.