Support Profiles

A 'profile' is a new concept for Prebid Server that aims to minimize data that needs to be sent on each request. Think of it as an account-specific small block of OpenRTB that gets merged into the main request.

See https://docs.google.com/document/d/1Fkwym4EREfOdaTD8SHUODKwlj-vWpZWQa0eGUToyzPU/edit?tab=t.0#heading=h.nkcbynukq4x0 for more details and the technical proposal.