feat(ui): add EnableNowPlaying configuration (default true) (#4219)

* Add EnableNowPlaying config option

* Return 501 for disabled NowPlaying

* chore(tests): remove get_now_playing_route test

* Disable now playing events when disabled

* fix(tests): add mutex for thread-safe access to scrobble buffer

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>

ui/src/eventStream.js

@@ -2,6 +2,7 @@ import { baseUrl } from './utils'
 import throttle from 'lodash.throttle'
 import { processEvent, serverDown } from './actions'
 import { REST_URL } from './consts'
+import config from './config'
 
 const newEventStream = async () => {
   let url = baseUrl(`${REST_URL}/events`)
@@ -33,7 +34,9 @@ const startEventStream = async (dispatchFn) => {
         throttledEventHandler(dispatchFn),
       )
       newStream.addEventListener('refreshResource', eventHandler(dispatchFn))
-      newStream.addEventListener('nowPlayingCount', eventHandler(dispatchFn))
+      if (config.enableNowPlaying) {
+        newStream.addEventListener('nowPlayingCount', eventHandler(dispatchFn))
+      }
       newStream.addEventListener('keepAlive', eventHandler(dispatchFn))
       newStream.onerror = (e) => {
         // eslint-disable-next-line no-console