Check `help_page_url` by documentation link linter

Related issue: https://gitlab.com/gitlab-org/gitlab/-/issues/208354
Previou implementation MR:
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/35351

**Problem**

The documentation link linter checks links defined by `help_page_path`
helper, however it ignores links from `help_page_url`.

**Solution**

Extend the pattern to match both `help_page_path` and `help_page_url`
helper methods