Offload image resizing from Magento

This work was initially done in scope of
https://jira.corp.magento.com/browse/ECP-261 and merged to 2.4-develop.
However, it was reverted later, before 2.4 release, in https://github.com/magento/magento2/commit/aabff222676aa2c8c040c31f8f245c90910ab365

AC:

• The commit is restored
• All tests pass

Original designs: https://wiki.corp.adobe.com/display/EntComm/Immutable+Filesystem+in+Magento (pending approval from @nrkapoor to be included here)

Discussion notes:

• Original URLs are part of SF and are not being delivered to core, so it's not breaking change for existing customers
• Not high-priority as it's expected that customers on Cloud have Fastly CDN, and it provides image transformation capabilities. PWA image URLs are compatible with Fastly image transformation URLs, so it should just work
• As first public step - document image transformation support for Fastly and an abstract CDN provider, so clients can be implemented in optimal way
• Continue working on design document to clarify strategy on image resizing for different scenarios (with CDN, w/o CDN)
• Review and prioritize the story as design is ready

Start by reviewing the reverted commit aabff222676aa2c8c040c31f8f245c90910ab365 and the linked design discussion. Confirm which image-resizing changes need restoration, then run the project test suite; done means the commit is restored and all tests pass.