[rpc] walletcreatefundedpsbt: don't automatically append inputs

When the user doesn't specificy inputs, it makes sense to automatically select them. But when the user does specify inputs, we now fail if the amount is insufficient, unless addInputs is set to true.

doc/release-notes-16377.md

@@ -0,0 +1,6 @@
+RPC changes
+-----------
+- The `walletcreatefundedpsbt` RPC call will now fail with
+  `Insufficient funds` when inputs are manually selected but are not enough to cover
+  the outputs and fee. Additional inputs can automatically be added through the
+  new `add_inputs` option.