CSM/SSM: Add on_mods_loaded callback (#7411)

* CSM/SSM: Add on_mods_loaded callback

src/script/cpp_api/s_server.h

@@ -30,6 +30,9 @@ class ScriptApiServer
 	// Returns true if script handled message
 	bool on_chat_message(const std::string &name, const std::string &message);
 
+	// Calls when mods are loaded
+	void on_mods_loaded();
+
 	// Calls on_shutdown handlers
 	void on_shutdown();