Support reviewer groups in Github

[La0]

Phabricator reporter is able to set specific reviewer groups on the revision when a specific linter fails.

Only the taskgraph diff task currently uses that feature.

The github reporter should support this feature, when the groups are available (ideally sharing the same name/slug as Phabricator)

[marco-c]

CC @shtrom, we might want to move this functionality in https://github.com/mozilla-conduit/reviewer-selector.

[shtrom]

CC @shtrom, we might want to move this functionality in https://github.com/mozilla-conduit/reviewer-selector.

Yep, that would be https://bugzilla.mozilla.org/show_bug.cgi?id=2040266 (and later iterations).