Pass in `app` as context to apply{N}Middleware
Pass in `app` as context to apply{N}Middleware

This lets us access registry config within middleware for additional
configuration of whatever it is that you're overriding.

Signed-off-by: Tony Holdstock-Brown <1001e8702733cced254345e193c88aaa47a4f5de@docker.com>

thaJeztah/distribution,thaJeztah/distribution