Add api key to configuration

MediaBrowser.Providers/Plugins/Tmdb/Configuration/PluginConfiguration.cs

@@ -7,6 +7,12 @@ namespace MediaBrowser.Providers.Plugins.Tmdb
     /// </summary>
     public class PluginConfiguration : BasePluginConfiguration
     {
+        /// <summary>
+        /// Gets or sets a value to use as the API key for accessing TMDb. This is intentionally excluded from the
+        /// settings page as the API key should not need to be changed by most users.
+        /// </summary>
+        public string TmdbApiKey { get; set; } = TmdbUtils.ApiKey;
+
         /// <summary>
         /// Gets or sets a value indicating whether include adult content when searching with TMDb.
         /// </summary>