feat: Add system_chainType to legacy rpcs (#2116)

* feat: Add system_chainType to legacy rpcs

* Test response

testing/integration-tests/src/full_client/client/legacy_rpcs.rs

@@ -118,6 +118,15 @@ async fn system_version() {
     let _ = rpc.system_version().await.unwrap();
 }
 
+#[subxt_test]
+async fn system_chain_type() {
+    let ctx = test_context().await;
+    let rpc = ctx.legacy_rpc_methods().await;
+
+    let chain_type = rpc.system_chain_type().await.unwrap();
+    assert_eq!(chain_type, "Development");
+}
+
 #[subxt_test]
 async fn system_properties() {
     let ctx = test_context().await;