Creating only one WS connection to pusher from admin

Also: migration to Typescript 4.5 and µWebsockets 1.20.4

pusher/src/Controller/InvalidTokenError.ts

@@ -0,0 +1,9 @@
+/**
+ * Errors related to variable handling.
+ */
+export class InvalidTokenError extends Error {
+    constructor(message: string) {
+        super(message);
+        Object.setPrototypeOf(this, InvalidTokenError.prototype);
+    }
+}