Add/Move helpers to register OBS websocket vendor requests

Adds websocket vendor requests to start and stop the plugin.
Adds vendor events to indicate when the plugin is started or stopped.

These are ntended to be used for the StreamDeck plugin support.

lib/utils/websocket-api.hpp

@@ -0,0 +1,17 @@
+#pragma once
+#include "export-symbol-helper.hpp"
+
+#include <functional>
+#include <obs-data.h>
+#include <string>
+
+namespace advss {
+
+EXPORT const char *GetWebsocketVendorName();
+EXPORT void RegisterWebsocketRequest(
+	const std::string &name,
+	const std::function<void(obs_data_t *, obs_data_t *)> &callback);
+EXPORT void SendWebsocketVendorEvent(const std::string &eventName,
+				     obs_data_t *data);
+
+} // namespace advss