Chromium Nightly cannot be selected via product selection UI

[stephenmcgruer]

Going to https://wpt.fyi/results/?label=experimental&label=master&aligned and hitting edit, there are only three options for Chrome's Channel: Stable, Beta, and Experimental. This means that Chromium Nightly runs can only be found via either the recent runs interface, or by knowing to pass label=nightly in the URL:

https://wpt.fyi/results/?label=nightly&label=master&product=chrome

We should make Chromium Nightly a fully supported product in our UI.