Docs: Fix section for Antora: "System Configuration and Customization"

Docs: Fix section for Antora: "System Configuration and Customization"

This commit does the known tasks to prepare each main docs section for
Antora:

  - Add chapter labels to nav file items
  - To match existing docs "chapter" level headings, combine adoc files as
    needed so that each "chapter" from the old docs structure has a single
    file linked from the nav
  - Upgrade all heading levels in each adoc file so that the top-most
    heading is a "Level 1" heading (example: "= Chapter Name =")
  - Add ":toc:" below top heading of each file

Signed-off-by: Remington Steed <rjs7@calvin.edu>