[auth] Use pyramid_multiauth
It makes it easier to finely tune what parts of the default authentication stack
we want to use or not.
It also makes it possible for any cube to add its own policy in addition to the
others.
Related to #4985962
include *.txt *.ini *.cfg *.rst
recursive-include sampleapp *.ico *.png *.css *.gif *.jpg *.pt *.txt *.mak *.mako *.js *.html *.xml