Add click-to-reveal cover for link previews on NSFW posts

A while ago the BE decided to disable link previews entirely for NSFW posts, but this should all be handled client/FE side as the metadata is available to choose how to deal with it. The FE already had code in there to disable images in link previews on NSFW posts, but we should make all of this consistent with image/video attachments

• Add click-to-reveal cover for the entire link preview
• Ensure it obeys user settings if they disable NSFW covers

You'll probably want to have this in your BE before you test: pleroma!3044 (merged)