Create a new draft post does not invalidate draft post count cache

[rayrfan]

Current behavior After you create a brand new draft, the post count number on the Draft in Admin > Posts is still cached and thus does not reflect the new draft count.

Steps to reproduce

1. Open blog composer and write a post
2. Save the post to a draft and close the composer

Expected behavior

When you create a brand new post to draft, it should invalidate the cache on StatsService.GetPostCountAsync

Additional notes Saving an already published post to a draft is no problem, it happens only on brand new post saved to draft.