policy: Add OP_1 <0x4e73> as a standard output type

These outputs are called anchors, and allow
key-less anchor spends which are vsize-minimized
versus keyed anchors which require larger outputs
when creating and inputs when spending.

src/rpc/util.cpp

@@ -332,6 +332,14 @@ public:
         return obj;
     }
 
+    UniValue operator()(const PayToAnchor& anchor) const
+    {
+        UniValue obj(UniValue::VOBJ);
+        obj.pushKV("isscript", true);
+        obj.pushKV("iswitness", true);
+        return obj;
+    }
+
     UniValue operator()(const WitnessUnknown& id) const
     {
         UniValue obj(UniValue::VOBJ);