openstack/devstack-plugin-ceph - devstack-plugin-ceph - OpenDev: Free Software Needs Free Tools

This patch enables building .pdf documentation using new 'pdf-docs'
tox environment. The newly created tox environment creates latex
source codes using sphinx-build and then builds the pdf
documentation using make.
Also, convert README.md to README.rst for more seamless integration
of the README file in the pdf and html documentation.
Story: 2006070
Task: 35457
Change-Id: I5c022478c9be0067c125efb4032c16cf0978330f

Switch to openstackdocstheme 2.2.1 and reno 3.1.0 versions. Using
these versions will allow especially:
* Linking from HTML to PDF document
* Allow parallel building of documents
* Fix some rendering problems
Update Sphinx version as well.
Set openstackdocs_auto_version to not auto-version the documents.
Set openstackdocs_auto_name to use 'project' as name.
openstackdocstheme renames some variables, so follow the renames
before the next release removes them. A couple of variables are also
not needed anymore, remove them.
Change pygments_style to 'native' since old theme version always used
'native' and the theme now respects the setting and using 'sphinx' can
lead to some strange rendering.
See also
http://lists.openstack.org/pipermail/openstack-discuss/2020-May/014971.html
Change-Id: I71e78d4ff18b0fd92f16f0917283eddad543250f

devstack-plugins-ceph does not have the doc infra set
up and no doc publish job.
This is need to add the contributor doc as per the ussuri
community goal.
Change-Id: Ib62c34b52b28b753f7f3046d51492fd8d9fb6193