**Add webhook event publishing for music state changes**

Introduced webhook event publishing to push music-state updates to a configured endpoint. Implemented `WebhookDispatcher` and `NoopEventPublisher` for dispatching events asynchronously or disabling them when no URL is set. Added handling of events like track start/end, queue updates, volume changes, and voice connection changes, enhancing integration with external systems.

.env.example

@@ -25,6 +25,8 @@ NETNEUTRALITY_WEBPO_URL=http://webpo:8080
 NETNEUTRALITY_WEBPO_PASSWORD=
 
 NETNEUTRALITY_SENTRY_DSN=
+NETNEUTRALITY_WEBHOOK_URL=
+NETNEUTRALITY_WEBHOOK_SECRET=
 GITEA_HOST=
 GITEA_TOKEN=
 GITEA_OWNER=