Document metrics dashboards in our wiki

Thanks mostly to @hiro's work we have a bunch of dashboards with useful data now. However, given that a lot of them have grown out of experimentation with the tooling and data there is a certain amount of "mushrooming" visible, which makes it hard to keep track of the important and useful dashboards. (Right now, I am fighting with a bunch of bookmarks in my browser for that, often forgetting where and whether we have data X visualized)

We should create something like metrics/dashboards in our wiki where we list our useful (could be experimental as well!) dashboards, explaining what they provide with links to them and to the scripts "sustaining" those dashboards.