In Zed cycle, we have dropped the python 3.6/3.7[1] testing
and its support. Add release notes and update the python
classifier for the same.
[1] https://governance.openstack.org/tc/reference/runtimes/zed.html
Co-Authored-By: Ghanshyam Mann <gmann@ghanshyammann.com>
Change-Id: I5c9dc8b1f72afa947679e36dd346e501a07980f6