Add release note for lockunspent change

doc/release-notes-23065.md

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+Notable changes
+===============
+
+Updated RPCs
+------------
+
+- `lockunspent` now optionally takes a third parameter, `persistent`, which
+causes the lock to be written persistently to the wallet database. This
+allows UTXOs to remain locked even after node restarts or crashes.
+
+GUI changes
+-----------
+
+- UTXOs which are locked via the GUI are now stored persistently in the
+wallet database, so are not lost on node shutdown or crash.