[Content editor][Back port] In preview show draft instead of published or unpublished version if it exists

In preview show draft instead of published or unpublished version if it exists

As a user
when I preview a document
and a draft exists
then I see the draft version
so that I am able to see if a change has to be made.

Note:
Currently the unpublished or published variant is shown. The contents of the fields can be different.

• log in as editor E
• Create a new document D
• save changes and publish the document
• edit the document
• logout
• login as admin A
• open the document

Observe that the published version is shown and not the contents of the draft.