Update octavia-tempest-plugin configref

This patch updates the octavia-tempest-plugin configuration reference
documentation to only include octavia-tempest-plugin specific
configuration options.
This simplifies our documentation and means bugs in other plugins will
not break our configuration reference docs job.

It also re-enables the docs job, disabled in a previous patch.

Change-Id: I53d81ca7bd910838927d594bfb0e72320b9d1ec6
diff --git a/setup.cfg b/setup.cfg
index 45e5030..ed187d4 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -29,3 +29,5 @@
 [entry_points]
 tempest.test_plugins =
     octavia-tempest-plugin = octavia_tempest_plugin.plugin:OctaviaTempestPlugin
+oslo.config.opts =
+    octavia-tempest-plugin = octavia_tempest_plugin.opts:list_opts