storage: Add a add_thread method:

This method is used to add a thread on an existing History record.

rel 457

libervia/backend/memory/sqla.py

@@ -731,6 +731,34 @@ class Storage:
                 f"Can't store message, unexpected exception (uid: {data['uid']}): {e}"
             )
 
+    @aio
+    async def add_thread(
+        self,
+        message_uid: str,
+        thread_id: str,
+        parent_id: str|None,
+        is_retroactive: bool,
+    ) -> None:
+        """Add a thread to a message.
+
+        @param message_uid: Internal ID of the message (History.uid) to which the thread
+            is added.
+        @param thread_id: The thread ID to set.
+        @param parent_id: The parent message ID in the thread.
+        @param is_retroactive: Whether the thread ID was added after the message was sent.
+            Is is used when we want to relate a parent message to a new thread, when the
+            parent message didn't have a thread ID initially.
+        """
+        async with self.session() as session:
+            thread = Thread(
+                thread_id=thread_id,
+                parent_id=parent_id,
+                is_retroactive=is_retroactive,
+                history_uid=message_uid,
+            )
+            session.add(thread)
+            await session.commit()
+
     ## Private values
 
     def _get_private_class(self, binary, profile):