Add missing content related tokens from Group Relationtionship Entity context.

Initial token addition commit patch.

I had a similar issue and created https://www.drupal.org/project/group_relationship_tokens → for that, maybe this could help here.

I've provided a new MR!197 with an approach that easily allows access to tokens of any related entity with a syntax like [group_relationship:entity:id] etc. where it doesn't matter what entity type the related entity actually has.

This is a duplicate of ✨ Group content tokens for label and referenced entity Needs review