Document extractor service (#15665)

* Document extractor service

* Fixing vendor modules

* Addressing PR Review comments

* Some small simplifications

* Fixing a linter complain

* simplifying a bit the code using package variables

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

vendor/github.com/ulikunitz/xz/make-docs

@@ -0,0 +1,5 @@
+#!/bin/sh
+
+set -x
+pandoc -t html5 -f markdown -s --css=doc/md.css -o README.html README.md
+pandoc -t html5 -f markdown -s --css=doc/md.css -o TODO.html TODO.md