Move the Save draft and Preview buttons to the product block header

[joshuatf]

The "Save draft" and "Preview" buttons should be moved over to the new product blocks header.

Precursor #37152.

Note that the above PR introduces the save button, but this may need to be tweaked to include the correct button labels.

The primary add/save button should publish the product (save the published product), similar to the post editor just with different labels.

Screenshots

Note that in the two pics below the Publish buttons has different labels as these are from GB, we should follow the labels from our design otherwise (this is mostly for the save draft design)

Acceptance criteria

• The preview button should open a new tab with the frontend preview (prior art exists in the previous iteration of the product editor)
• The "Save" button should say "Save" for existing products and "Add" for new products (auto-drafts), but should publish the product
• The "Save draft" should follow the Gutenberg post format (see above screenshots), say Save draft if edited and draft status, show Switch to draft if published, show Saved if draft and saved (no edits).