Consider hiding or annotating metrics sent in pings not defined in the application

e.g. [this metric](https://dictionary.telemetry.mozilla.org/apps/fenix/metrics/characteristics_font_minimum_size_default_group) is defined and collected in `gecko`, but the ping it's submitted in ("user-characteristics") is only defined in `firefox_desktop`

This can be confusing because 1) It's not actually there, and 2) All the links for exploring the data do not work