Enable testing beta RPC API version with config

src/ripple/core/impl/Config.cpp

@@ -635,6 +635,9 @@ Config::loadFromString(std::string const& fileContents)
                 "majority is 15 minutes");
     }
 
+    if (getSingleSection(secConfig, SECTION_BETA_RPC_API, strTemp, j_))
+        BETA_RPC_API = beast::lexicalCastThrow<bool>(strTemp);
+
     // Do not load trusted validator configuration for standalone mode
     if (!RUN_STANDALONE)
     {