setup.cfg: Replace dash-separated config

Resolve the following warnings like the following being issued when
building the package:

  UserWarning: Usage of dash-separated 'description-file' will not be
  supported in future versions. Please use the underscore name
  'description_file' instead

Change-Id: I4b75aac2c09b772f91e5ac9a4e77e9462f38bfd1
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

setup.cfg

@@ -1,25 +1,31 @@
 [metadata]
 name = osc-lib
 summary = OpenStackClient Library
-description-file =
+description_file =
     README.rst
 author = OpenStack
-author-email = openstack-discuss@lists.openstack.org
+author_email = openstack-discuss@lists.openstack.org
-home-page = https://docs.openstack.org/osc-lib/latest/
+url = https://docs.openstack.org/osc-lib/latest/
-python-requires = >=3.6
+project_urls =
+    Bug Tracker = https://storyboard.openstack.org/#!/project/openstack/osc-lib
+    Documentation = https://docs.openstack.org/osc-lib/latest/
+    Source Code = https://opendev.org/openstack/osc-lib/
+python_requires = >=3.6
 classifier =
+    Development Status :: 5 - Production/Stable
     Environment :: OpenStack
     Intended Audience :: Information Technology
     Intended Audience :: System Administrators
     License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
     Programming Language :: Python
-    Programming Language :: Python :: Implementation :: CPython
-    Programming Language :: Python :: 3 :: Only
     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 :: 3.10
+    Programming Language :: Python :: 3 :: Only
 
 [files]
 packages =