fix(config): restored deleted code

I accidently deleted some cacheing mechanisms, these have been restored

src/config/private/config.cpp

@@ -29,4 +29,14 @@ bool Config::loadConfig(const std::string& configFile) {
     return true;
 }
 
+bool Config::isKeyInCache(const std::string &key) {
+    return configMap.find(key) != configMap.end();
+}
 
+void Config::addToCache(const std::string &key, const YAML::Node &node) {
+    configMap[key] = node;
+}
+
+void Config::registerUnknownKey(const std::string &key) {
+    unknownKeys.push_back(key);
+}