Use a Guid to uniquely identify migrations instead of a string name

Also use a list instead of an array to store executed migrations in the configuration class

Jellyfin.Server/Migrations/Routines/DisableTranscodingThrottling.cs

@@ -12,6 +12,9 @@ namespace Jellyfin.Server.Migrations.Routines
     /// </summary>
     internal class DisableTranscodingThrottling : IMigrationRoutine
     {
+        /// <inheritdoc/>
+        public Guid Id => Guid.Parse("{4124C2CD-E939-4FFB-9BE9-9B311C413638}");
+
         /// <inheritdoc/>
         public string Name => "DisableTranscodingThrottling";