docs: policies page in the admin guide needs an update

[Brian Rosmaita]

The page still refers to the v1 API, so those things can go. Additionally, some of the descriptions are misleading, for example,

    publicize_image - Create or update public images

That permission really only has to do with the image visibility, I'm pretty sure the image owner can always update the "reglar" properties on a public image.

It would also be nice to say something about the policy filename, where it should go, etc., something like cinder has at the top of this page:

https://docs.openstack.org/cinder/latest/configuration/block-storage/samples/policy.yaml.html

-----------------------------------
Release: 25.0.0.dev67 on 2020-11-24 16:30:47
SHA: 39b44ce1cca0cb3cdb95248b589e0f55fd421856
Source: https://opendev.org/openstack/glance/src/doc/source/admin/policies.rst
URL: https://docs.openstack.org/glance/latest/admin/policies.html

[Takashi Kajinami (kajinamit)]

Thanks Brian to raising this.

I'd like to express my +1 for that description of the publicize_image policy at least, based on the confusions we noticed during our discussion in ml .