Add auto-draft to list of statuses faked in get_sample_permalink()

[earnjam]

In the new editor, we currently have to wait for a manual save or publish in order to edit the permalink. I'm working on resolving this in ​https://github.com/WordPress/gutenberg/pull/12009. To facilitate immediate editing of the permalink, we need to know the permalink structure at the time the editor is initialized.

#45017 added added the permalink_template to the REST posts controller. The solution there uses get_sample_permalink() to generate the permalink_template value. This works for certain non-published post statuses by faking the post status to publish when running get_permalink().

However, when we initialize a new post in the block editor, the status is auto-draft. So it returns a standard non-pretty permalink in the format /?p=123. We don't know the permalink structure until a draft is manually saved, or the post is published.

By adding auto-draft to this list of statuses that are faked as published, it will return the proper permalink_template for auto-draft posts.