Overhaul Python package metadata

Modernize our package metadata in the following ways:

* switch from description-file to long_description with the file
  attribute, and specify an explicit content type and encoding

* replace the home-page parameter with the newer general url one

* add specific labelled project links for improved navigation from
  PyPI's summary sidebar

* include some appropriate keywords to help folks searching

* use the specific license metadata in addition to the corresponding
  trove classifier for it

* make sure wheels when built also incorporate the LICENSE and
  AUTHORS files so that we're not distributing them without a copy
  of the license text

* add a few more relevant trove classifiers, and clarify that this
  tool is intended to be platform-independent

* move the python-requires metadata into the options block

https: //setuptools.readthedocs.io/en/latest/userguide/declarative_config.html

Change-Id: I0df0f6575e2bfc20b37eb82c258212d5f1a59129

setup.cfg

@@ -1,22 +1,44 @@
 [metadata]
 name = zuul-client
 summary = A client for the Zuul Gating System
-description-file =
-    README.rst
+long_description = file: README.rst
+long_description_content_type = text/x-rst; charset=UTF-8
 author = Zuul Team
 author-email = zuul-discuss@lists.zuul-ci.org
-home-page = https://zuul-ci.org/
-python-requires = >=3.6
+url = https://zuul-ci.org/
+project_urls =
+    Browse Source = https://opendev.org/zuul/zuul-client
+    Bug Reporting = https://storyboard.openstack.org/#!/project/zuul/zuul-client
+    Documentation = https://zuul-ci.org/docs/zuul-client
+    Git Clone URL = https://opendev.org/zuul/zuul-client
+    License Texts = https://opendev.org/zuul/zuul-client/src/branch/master/LICENSE
+    Release Notes = https://zuul-ci.org/docs/zuul-client/releasenotes.html
+keywords = gating continuous integration delivery deployment commandline
+license = Apache License, Version 2.0
+license_files =
+    AUTHORS
+    LICENSE
 classifier =
+    Environment :: Console
     Intended Audience :: Information Technology
     Intended Audience :: System Administrators
     License :: OSI Approved :: Apache Software License
-    Operating System :: POSIX :: Linux
+    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
+    Topic :: Software Development :: Quality Assurance
+    Topic :: Software Development :: Testing
+    Topic :: Software Development :: Version Control :: Git
+    Topic :: System :: Systems Administration
+    Topic :: Utilities
+
+[options]
+python-requires = >=3.6
 
 [files]
 packages = zuulclient