Add a CTA to the unpublished lessons notice

[donnapep]

Is your feature request related to a problem? Please describe

A notice is displayed on the frontend when previewing a course that contains no published lessons. This notice does not provide the user with next steps to take.

Note: There are actually two notices (see screenshots below). I don't know why we have notices, but I think we should be able to simplify down to a single notice.

Describe the solution you'd like

Update the notice to the following text, where clicking on "your lessons" takes the user to the Lessons page (wp-admin/edit.php?post_type=lesson) in WP admin, filtered by the current course and by Draft status.

When you're ready, let's publish your lessons in order to make them available to your students. Unpublished lessons are only visible in preview mode.

Nice-to-have: It would be nice to left-align the notice text. This isn't a mandatory requirement for this issue though. I imagine it will affect all notices (which is probably a good thing).

Additional context

Current Notice #1

Current Notice #2

Desired Notice

[renatho]

Note: There are actually two notices (see screenshots below). I don't know why we have notices, but I think we should be able to simplify down to a single notice.

I think we'll need both anyway because of the notice for the students. For them, I imagine the "Current Notice 1" is probably enough for any situation, because it's just informative and they don't need to take any action.