LP#1848524: various fixes

LP#1848524: various fixes

* Fix syntax broken by "heading conversion" script
* Improve antora navs, add missing attrib files
  - Remove numbering from install docs headers
  - Link top-level nav items to each section's intro file
  - Add a few missing _attributes.adoc files in pages/ subdirs
* Start converting internal links to antora format

  Links to sections in the same file only need the section ID like this:

  xref:#section_id

  But links to sections in another file need the Antora page_id also:

  xref:MODULE:PAGE.adoc#section_id

* Convert existing anchors to Antora syntax
* Convert more links to Antora syntax

Antora requires that links to sections in a different file use the xref
syntax, not the double-angle-bracket shortcut syntax. As best as I can
tell, this commit changes all the links that go to other files (not the
file that the link is in).

Signed-off-by: Remington Steed <rjs7@calvin.edu>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>