This reimplements our Zoom video call integration to use an OAuth
application. In addition to providing a cleaner setup experience,
especially on zulipchat.com where the server administrators can have
done the app registration already, it also fixes the limitation of the
previous integration that it could only have one call active at a time
when set up with typical Zoom API keys.
Fixes#11672.
Co-authored-by: Marco Burstein <marco@marco.how>
Co-authored-by: Tim Abbott <tabbott@zulipchat.com>
Signed-off-by: Anders Kaseorg <andersk@mit.edu>