team-stats does not fully support adhoc-group

[Mark-Simulacrum]

In rust-lang/rust the adhoc-group for library/ code is:

https://github.com/rust-lang/rust/blob/5f36a7f8072e835d73d9e1f7ab8a2134ac7352dc/triagebot.toml#L1476-L1484

    "@Mark-Simulacrum",
    "@workingjubilee",
    "@jhpratt",
    "@tgross35",
    "@thomcc",
    "@ibraheemdev",
    "@joboet",

All of these people are not on the T-libs team (most are in libs-contributors, maybe all), so when a team-stats libs is issued, they are not present in the response.

I think what we'd want to do is extend the members list (or perhaps have a stats-for-file with an argument that can be a file in the repo?) with the adhoc-group's members.

[Kobzol]

I think we can just add a switch, something like --group team/adhoc. Or should we combine both the team and the adhoc team in the output? 🤔 But that doesn't make much sense w.r.t. review capacity, because the adhoc group overrides the team in r?.