docs: add memory how-tos + update add_messages (#958)

---------

Co-authored-by: vbarda <vadym@langchain.dev>

docs/_scripts/copy_notebooks.py

@@ -25,7 +25,9 @@ _MANUAL = {
         "streaming-events-from-within-tools.ipynb",
         "streaming-from-final-node.ipynb",
         "persistence.ipynb",
-        "managing-conversation-history.ipynb",
+        "memory/manage-conversation-history.ipynb",
+        "memory/delete-messages.ipynb",
+        "memory/add-summary-conversation-history.ipynb",
         "persistence_postgres.ipynb",
         "visualization.ipynb",
         "state-model.ipynb",