Pbr is a very heavy package to depend on. It requires git-core, which is
16 MiB on my Fedora. We only use it to detect the version, which can be
done without pbr using a much lighter importlib_metadata.

Copied from https://review.opendev.org/c/openstack/osprofiler/+/739379

Change-Id: I5f434e6bfde6f645804941f3a36d5458a28270e7

This adds and configures a sphinx doc builder. This is based on the code
in Ironic to build documentation.

The goal is for this to contain development documentation relevant to
hacking on the agent, including how to make custom HardwareManagers.

Change-Id: Ib6cecb9959f4ad5c71440fb37827b996582a9545