add a service to return all entities attached to a specific wallet

[levalleux-ludo]

At the moment, there are ways to retrieve:

• a seller based on a wallet address
• OR a buyer based on a wallet address
• OR a DR based on a wallet address

The idea of such a new service would allow to return all entities (seller, buyer, DR, agent, ...) related to a given wallet address, in only 1 call.
Ideally the subgraph should represent this "attachment" so that a simple graphQL request would return all the entities