Add support for group membership synchronization

We try to setup the group synchronisation as written in configuration guide with the claim "xwiki_user_groups". While our provider (we use keycloak) returns the value in both userinfo and id_token, the groups are not imported.

I am not sure if the feature is intended to be use this way, while reading the code I can find any clue of the user groups being read, the only attribute to be matched is "CLAIM_XWIKI_GROUPS" defined __ as "xwiki_groups", we tryed to bind this attribute also but no result.

Could you tell me if the feature is supposed to be used this way or if we have a misunderstanding.