docs: add a how-to on subgraph transform state (#1595)

* docs: add a how-to on subgraph transform state

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Co-authored-by: isaac hershenson <ihershenson@hmc.edu>
Co-authored-by: Isaac Francisco <78627776+isahers1@users.noreply.github.com>

docs/_scripts/copy_notebooks.py

@@ -31,6 +31,7 @@ _MANUAL = {
         "pass_private_state.ipynb",
         "memory/manage-conversation-history.ipynb",
         "subgraphs-manage-state.ipynb",
+        "subgraph-transform-state.ipynb",
         "memory/delete-messages.ipynb",
         "memory/add-summary-conversation-history.ipynb",
         "persistence_postgres.ipynb",