US2807 - Add docs that explain how to configure Pulp to work with a given broker config.

The intent of this story is about configuring Pulp to work with a given broker config, and not about configuring the broker for a given config. Assuming the user has a specific Qpid or RabbitMQ installation in place, this guide can tell them how to do the Pulp portion.

I originally wrote the settings for the [task] section, so I can vouch for their correctness. I believe the [messaging] section is correct, but I had to read up on those settings, along with some notes I got from @jortel.

One known gap is that it doesn't talk much about the rpm installation for Qpid transport. I have a future PR planned that is going to fill that gap through the creation of a new groupinstall command. That is considered separate work.

I also fixed a few docs errors that were causing warnings and errors. With this PR docs built from scratch will experience no syntax errors or warnings.
In the past, we've just documented these in-line in the example config file. Having these options defined in only one place prevents divergence when someone forgets to update multiple documents. What do you think about mentioning where to find these settings, but leaving their actual documentation in-line in the config file?