feat(watchlist): Cache watchlist requests with matching E-Tags (#3901)

* perf(watchlist): add E-Tag caching to Plex watchlist requests

* refactor(watchlist): increase frequency of watchlist requests

* fix: sync watchlist every 3 min instead of 3 sec

server/lib/settings.ts

@@ -407,7 +407,7 @@ class Settings {
           schedule: '0 0 3 * * *',
         },
         'plex-watchlist-sync': {
-          schedule: '0 */10 * * * *',
+          schedule: '0 */3 * * * *',
         },
         'radarr-scan': {
           schedule: '0 0 4 * * *',