docs: Prohibit 'external' links within the webpage

Enforce that relative links are used within the page, so that local
installations don't require internet conection and/or don't redirect to
the web needlessly.

This is done by looking for any local link (barring exceptions) when
checking links with 'check-html-references.py'.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

docs/meson.build

@@ -359,6 +359,9 @@ if tests_enabled[0]
     args: [
       check_html_references_prog.full_path(),
       '--require-https',
+      '--project-uri', 'https://libvirt.org',
+      '--project-uri-exceptions', 'docs/manpages/',
+      '--project-uri-exceptions', 'docs/html/',
       '--webroot',
       meson.project_build_root() / 'docs'
     ],