Improve userInGroup to make it more efficient and able to search across nested groups

[sneko]

I hope it will help others :)

[sneko]

Here an old related issue: bitly#358

@eskilandreen @snomann @framillien maybe you're still interested in :)

[ploxiln]

Very nice!
I'm going to squash-n-merge in order to tweak the commit title and message, I hope that's fine with you.

[sneko]

Sure go ahead! :)

[sneko]

@ploxiln just to follow up:

There is an issue with members that are outside the group domain (means a bug with @gmail.com in a @domain.com group).

I just discovered that. That's something on Google side but I can't figure out if this is the wanted behavior... It seems so strange.

For now they didn't answer to the issue someone has posted: https://issuetracker.google.com/issues/109861216

I will keep you updated. If they don't fix the bug I think we have to forget about using subgroups and get back to the old loops over group members 😢

EDIT: a possible way with the old way before this PR would be to set to true the "includeDerivedMembership" (https://developers.google.com/admin-sdk/directory/v1/reference/members/list). But I guess the pagination limit would be present.