[docs] Restructure and refactor beats documentation

[dedemorton]

Breaks the configuration section down into two separate sections. Also adds abbreviated titles to make the TOC easier to scan.

To do:

• Apply structural changes to all Beats books.
• Make config section order. consistent across all the books
• Make titles consistent (use configure instead of set up in config section).
• Make sure functionbeat sections are correctly flagged as xpack.
• Do diff across all books to verify that nothing was dropped.
• Do final check on files for consistency, etc.
• Hold on merging until Brandon M. approves.

Assuming the build succeeds, you can preview the new navigation structure here:

http://beats_16825.docs-preview.app.elstc.co/diff

[dedemorton]

I've tried to arrange the configuration section in what I perceive to be "logical" order (putting the settings users are likely to want to know about or set up stuff early on).

[dedemorton]

@benskelker @bmorelli25 Just a heads-up that I'm doing some restructuring of the config section of the Beats documentation. After I get the nav structure ironed out, I am going to do some file refactoring (will rename and move a bunch of stuff). I'll probably do that in a separate PR, though.

[benskelker]

@dedemorton thanks for the heads up

[bmorelli25]

Overall, I think these changes look great! Love the new layout, and love how easy it is to browse the TOC because of the new <titleabbrev> 🔥!! I've left a few comments and questions below. Although I've only tagged one example, most comments apply to all Beat books. A couple of the comments are specific to just one book.

[bmorelli25]

LGTM