Add XML docs to small channel types and remove CS1591 suppressions

MediaBrowser.Controller/Channels/IHasCacheKey.cs

@@ -1,14 +1,15 @@
-#pragma warning disable CS1591
-
 namespace MediaBrowser.Controller.Channels
 {
+    /// <summary>
+    /// Interface for channels that provide a cache key.
+    /// </summary>
     public interface IHasCacheKey
     {
         /// <summary>
         /// Gets the cache key.
         /// </summary>
         /// <param name="userId">The user identifier.</param>
-        /// <returns>System.String.</returns>
+        /// <returns>The cache key.</returns>
         string? GetCacheKey(string? userId);
     }
 }