rpcserver: expose interceptor required flag on info call

lnrpc/lightning.swagger.json

@@ -4445,6 +4445,10 @@
             "$ref": "#/definitions/lnrpcFeature"
           },
           "description": "Features that our node has advertised in our init message, node\nannouncements and invoices."
+        },
+        "require_htlc_interceptor": {
+          "type": "boolean",
+          "description": "Indicates whether the HTLC interceptor API is in always-on mode."
         }
       }
     },