Add air-gapped install docs (#2458) (#2482)

* Add structure

* Part 1 and 2 content

* add appendices, mostly

* Add How to Configure sections

* Clean-up

* Use variable attributes in place of hard-coded version numbers

(cherry picked from commit 2e16b69)

Co-authored-by: David Kilfoyle <[email protected]>

Author: mergify[bot]