Add embed code option allowing to autoplay DAM videos

Introduced new embed code called "Background video" which allow to video to autoplay with muted, loop, playsinline.
Please review.

MR's of new features should target the 1.1.x branch.

capysara → changed the visibility of the branch 3377497-add-embed-code to hidden.

Created MR against 1.1.x

In general terms, I like the idea, thanks for bringing it up and creating an MR. Some objectives from me:

• The naming of the new option should fit into the semantical pattern of already existing ones, which mostly (all?) describe what the editor will receive when choosing that option (eg. “inline_view”, “link_thumbnail_download”, and “link_thumbnail”). Oppositely, the suggested name “background_video” represents a possible purpose for how this option can be used.
  
  After some testing, I found the proposed setup very similar to the already existing “video_stream” option. Therefore I suggest we could help the content editors understand better the difference between these two.
• The autoplay feature activates within the WYSIWYG editor as well. I did not started to investigate any possibilities to its specific disablement, so we can handle it as a known issue until hearing back end-user complaints.

I think its a good incremental step forward. Committed