change(docs): Consolidate the docs for configuring Zebra

[upbqdn]

Motivation

I was looking up the possible locations of the config file and some basic config options in the user docs, and I realized this information is scattered around and repeated in multiple places. I'd find it useful to have a separate subsection dedicated to configuring Zebra.

Solution

• Create a subsection "Configuring Zebra" and place it between "Installing Zebra" and "Running Zebra".
• Move the content related to configuring Zebra from other subsections to the new one.