* build: add just modules

A lot of our build recipes share similar structures. Move some of
these to modules so we can control them centrally.

* build: add Makefile deprecation helper

This allows us to implement deprecated Makefiles as:

  DEPRECATED_TARGETS := ...
  include ../just/deprecate.mk

* build(docker): add just modules to docker context

We need to make sure our build framework is included in the docker build
context.
Also make sure just is part of the builder image.

* build(op-batcher): migrate build to just