Implement nextgen random handler and tests (#576)

Fixes #575

unittests/rpc/handlers/PingTest.cpp

@@ -23,12 +23,12 @@
 
 using namespace RPCng;
 
-class RPCHandlerTest : public NoLoggerFixture
+class RPCPingHandlerTest : public NoLoggerFixture
 {
 };
 
 // example handler tests
-TEST_F(RPCHandlerTest, Ping)
+TEST_F(RPCPingHandlerTest, Default)
 {
     auto const handler = AnyHandler{PingHandler{}};
     auto const output = handler.process(boost::json::parse(R"({})"));