[Product thumbnail] Media position and lazy load

[andrewetchen]

Captured improvements for product-thumbnail snippet:

• Update product-thumbnail to remove the <modal-opener> structure from video and model medias since the right columns layout on mobile is never used.
  • This issue was created based on Lucas' feedback from: [Product layout] Add desktop media position #1720 (comment)

    We can revisit this in a separate follow up PR, but I would suggest adding a variable to product-thumbnail to remove <modal-opener> structure from video and model medias.

• Update lazy load logic when using columns layout
  • This issue was created based on Ludo's feedback from:[Product page] Add 2 column layout for desktop and mobile #1766 (review)

    I think it could be useful to change the logic to be based on the number of columns instead of the 1 used. This way we can tell the two/three first images to not lazy load.