Add ability to configure asciidoctor extensions to run during body (default),...

Add ability to configure asciidoctor extensions to run during body (default), header, and nav processing.
3 jobs for issue-592-nav-header-extensions in 4 minutes and 8 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Init
passed #746950551
yarn

00:01:11

 
  Verify
passed #746950552
lint

00:01:14

passed #746950553
test

00:02:57