New: Drop commands table content before postgres migration

Signed-off-by: Stevie Robinson <stevie.robinson@gmail.com>
(cherry picked from commit 8dd3b45c90209136c0bd0a861061c6d20837d62f)

Closes #3225

src/NzbDrone.Core/Datastore/Migration/023_postgres_update_timestamp_columns_to_with_timezone.cs

@@ -8,6 +8,8 @@ namespace NzbDrone.Core.Datastore.Migration
     {
         protected override void MainDbUpgrade()
         {
+            Delete.FromTable("Commands").AllRows();
+
             Alter.Table("Authors").AlterColumn("LastInfoSync").AsDateTimeOffset().Nullable();
             Alter.Table("Authors").AlterColumn("Added").AsDateTimeOffset().Nullable();
             Alter.Table("AuthorMetadata").AlterColumn("Born").AsDateTimeOffset().Nullable();