Implement public cohort

This PR is based on #19284 and is part of the
series of work related to the proposal #18134.

This PR avoids the assignment of
anonymous/unenrolled users to any cohort when
course is public. Anonymous or unenrolled users
will only see content that does not have a
content group assigned.
The "View Course" link to the course outline
is shown on the course about page for a course
marked public/public outline.
It also makes course handouts available for
public courses (not for public_outline).
This PR also hides the different warnings and
messages asking the user to sign-in and enroll
in the course, when the course is marked public.
It modifies the default public_view text to
include the component display_name when
unenrolled access is not available.