[Gekidou] [Migration] Adds member_count to groups table (#6468)

* Adds member_count to groups table

* Newline

types/api/groups.d.ts

@@ -8,7 +8,7 @@ type Group = {
     description: string;
     source: string;
     remote_id: string;
-    member_count: number;
+    member_count?: number;
     allow_reference: boolean;
     create_at: number;
     update_at: number;

types/database/models/servers/group.d.ts

@@ -43,6 +43,9 @@ export default class GroupModel extends Model {
     /** deleted_at : The timestamp for when it was deleted */
     deletedAt: number;
 
+    /** member_count : The number of members in the group */
+    memberCount: number;
+
     /** channels : All the channels associated with this group */
     @lazy channels: Query<ChannelModel>;