OAuth: return github teams as a part of user info (enable team sync) (#17797)

* OAuth: github team sync POC

* OAuth: minor refactor of github module

* OAuth: able to use team shorthands for github team sync

* support passing a list of groups via auth-proxy header

pkg/api/login_oauth.go

@@ -171,6 +171,7 @@ func (hs *HTTPServer) OAuthLogin(ctx *m.ReqContext) {
 		Login:      userInfo.Login,
 		Email:      userInfo.Email,
 		OrgRoles:   map[int64]m.RoleType{},
+		Groups:     userInfo.Groups,
 	}
 
 	if userInfo.Role != "" {