Have ldap:AttributeAddUsersGroups support ldap:LdapMulti

Hi, I noted that in the docs for ldap:AttributeAddUsersGroups, it is clearly stated:

Note: ldap:LdapMulti is not supported as the SimpleSAMLphp framework does not pass any information about which LDAP source the user selected.

And I understand that if you do have multiple LDAP instances, you can place your ldap:AttributeAddUsersGroups configuration in the service provider metadata and in that way control which LDAP instance is queried for groups when a user attempts to access a particular service.

But I do wonder if there is any appetite for adding support for ldap:LdapMulti? So that with ldap:AttributeAddUsersGroups configuration in the IdP metadata, groups will be queried from the authentication source (organisation) the user selected?

I'd be very happy to work on this if anyone feels it would be a useful feature to add.

まず docs/ldap.md と ldap:AttributeAddUsersGroups セクションを確認し、文書化されている制限を理解します。次に、IdP メタデータと選択された認証ソースがどのように表現されているかを追跡します。この issue ではフレームワーク情報の不足が指摘されていますが、実装のエントリーポイントやテストは示されていません。完了には、合意された設計、ldap:LdapMulti のサポート、ドキュメントの更新が必要です。