List groups

The group conversations your lines belong to. A group is a conversation that isn't a phone number, so Dial gives it an ID of its own; you address it with `groupId` on Send a message and filter for it on List messages. Groups exist on WhatsApp lines today. **`name` may be `null`, which is not an error.** Participants rename groups, so Dial stores no copy of the subject — it is read live from the line that holds the conversation. A line that can't answer in time yields `name: null` for its groups rather than failing the request, so one unreachable line never hides another line's groups. Your line must already be a member: Dial can send into a group your number was added to, but cannot create one, join one, or accept an invite link. There is no join event — a group your line was just added to shows up as a new entry here.