MVP completed: Hook into Playlistmanager to post updates to beatleader maps owned by the user

Setlist/SetlistSyncHost.cs

@@ -0,0 +1,32 @@
+using BeatSaberPlaylistsLib.Types;
+using UnityEngine;
+using IPALogger = IPA.Logging.Logger;
+
+namespace Setlist
+{
+    /// <summary>
+    /// Persists for <see cref="UnityEngine.MonoBehaviour.StartCoroutine"/> (e.g. BeatLeader POST after UI adds a song).
+    /// </summary>
+    internal sealed class SetlistSyncHost : MonoBehaviour
+    {
+        internal static SetlistSyncHost Instance { get; private set; }
+
+        internal static void Ensure()
+        {
+            if (Instance != null)
+            {
+                return;
+            }
+
+            var go = new GameObject("Setlist.SyncHost");
+            UnityEngine.Object.DontDestroyOnLoad(go);
+            go.hideFlags = HideFlags.HideAndDontSave;
+            Instance = go.AddComponent<SetlistSyncHost>();
+        }
+
+        internal void StartPostOwnedBeatLeaderPlaylist(IPlaylist playlist, IPALogger log)
+        {
+            StartCoroutine(BeatLeaderPlaylistSync.CoPostOwnedPlaylistToBeatLeader(playlist, log));
+        }
+    }
+}