docs: add release notes for 31603

Author: brunoerg

doc/release-notes-31603.md

@@ -0,0 +1,6 @@
+Updated RPCs
+--------
+
+- Any RPC in which one of the parameters are descriptors will throw an error
+if the provided descriptor contains a whitespace at the beginning or the end
+of the public key within a fragment - e.g. `pk( KEY)` or `pk(KEY )`.