Byline images in blocks are not responsive

[marsavar]

If we want to upgrade to responsive images (picture/source/srcset) on DCR we need to:

• Make a PR to frontend to generate them and send them through (DCR can't do this atm because it requires access to the "salt" for signed URLs)
• Update the DCR model to pass through this new data to the component
• Update the component API to accept the different srcsets

AR already has these srcsets, so they can be passed through then too.

Originally posted by @JamieB-gu in #4369 (comment)