Telescopetest-io: add information/explanation for metrics

It would be nice to have info cards/small descriptions on telescopetest-io explaining things like what metrics mean, how they were calculated, how to use certain visualizations, where metrics come from in the actual results files, etc.

Start by locating the telescopetest-io metric visualizations and the code that reads metrics from actual results files. Define the set of metrics and visualizations needing explanations, then add info cards or descriptions that explain their meaning, calculation, source, and use; done means the relevant metrics are understandable in the interface.

Written by the indexing model from the issue text.