perf(config): added cache

In order to prevent traversing the YAML tree I have added a hash map (O(1) lookup) to cache already accessed config variables. I have also added a vector to store keys requested but not found so we do not need to check for those every time

src/config/private/config.cpp

@@ -29,3 +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);
+}