[Feature Proposal][PR Attached] Fallback to JPEG instead of PNG for non web images if they are opaque

Active Storage representations currently falls back to PNG if the image blob is not in the web_image_content_types . While this ensures that the images are viewable in any browser, it generates rather large files that can eat through users data plans if they are viewing a large gallery, and make the page take much longer to load than necessary.

My proposal is to add opaqueness detection to the image analyzers and uses JPEG as the fallback instead.

I’ve prepared a PR to help discussion: