Remove participants from ConversationType

[spolu]

The list of participants is currently computed server side in lib/api but really it can be computed from the conversation so it should not exist on the ConversationType as it does not bring any new capability, it's just a convenience for our product to have it here.

Let's either move its computation fully client-side or create separate endpoints to compute them and have access to them. Both are fine.

[PopDaph]

@spolu was about to start this task but I have a second thought.

There is no additional query to fetch the list of participant, we just take advantage of a loop on messages in getConversation to fill the list of participants, and return them: https://github.com/dust-tt/dust/blob/main/front/lib/api/assistant/conversation.ts#L404

So I think we shouldn't change the way it's done. OK for you?

[spolu]

Well the only tension is for the public API this field really is not needed. What is the rationale for keeping it server-side versus moving the logic client-side? The rationale I see for doing it is simplifying the object we return from GET /.../conversations/[cId]

[PopDaph]

#1935 🙇🏻‍♀️