Link from monitoring page to connector-specific metrics

Currently there's no link from the main monitoring page to the description of individual metrics in the specific connector docs. As the metrics are largely the same, it might be the best to extract them to the monitoring page, so that it has all the info in one place. And then on connector pages maybe a link to that one.

Mostly unrelated, but another doc issue: the right-hand side menu's top-level items look odd when wrapped around to two lines; the second line has less indentation then the first line then. That is only the case for the top-level menu hierarchy, lower levels are consistently indented.