Drop python3.6/3.7 support in testing runtime

In Zed cycle testing runtime, we are targetting to drop the
python 3.6/3.7 support, project started adding python 3.8 as minimum,

example nova:
- 56b5aed08c/setup.cfg (L13)

Also moving zuul's job to zed

Change-Id: I43aa0f2a571f5a4f2bb31c58a3e287b519dd48bf

.zuul.yaml

@@ -4,9 +4,7 @@
       # FIXME: see https://review.opendev.org/747460
       # - lib-forward-testing-python3
       - openstack-cover-jobs
-      # FIXME: add lower-constraints or drop this
-      # - openstack-lower-constraints-jobs
-      - openstack-python3-wallaby-jobs
+      - openstack-python3-jobs
       - periodic-stable-jobs
       - publish-openstack-docs-pti
       - release-notes-jobs-python3

setup.cfg

@@ -6,7 +6,7 @@ description_file =
 author = OpenStack
 author_email = openstack-discuss@lists.openstack.org
 home_page = https://docs.openstack.org/etcd3gw/latest/
-python_requires = >=3.6
+python_requires = >=3.8
 classifier =
     Environment :: Console
     Environment :: OpenStack
@@ -16,8 +16,6 @@ classifier =
     Operating System :: OS Independent
     Programming Language :: Python
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.6
-    Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3 :: Only