Replace the group/stage with the documentation title as the sources link text

Some of Sources in the answer of the GitLab Chat shows none/none. The possible reason is that we return the stage/group in the header of the documentation file. And when that information is missing from the file, we render none/none. So, the suggestion is to use other information, like page title, as the link text.

Per @dgruzd, We use metadata from the header. Using title is a good idea, but we need to use a markdown parser to inject that into existing data. Current dataset is a copy from the PoC since we don't have Ruby indexer implemented yet