We are talking about two different types of documentation:
* Infrastructure Docs
Just like the rest of WMF infrastructure the lawful place for this is wikitech. It is documentation technical in nature of interest to engineers working at the WMF mostly. It makes sense most people do not know about it, you wouldn't unless you have worked for WMF or committed code in a volunteer capacity.
*Metrics definitions
Our metrics are not different from research's metrics, we execute on metrics researchers have defined. If research wants to keeps those in meta I think it should not be a problem.