Is PROJECT_SENTRY from constants.py necessary?

[clarmso]

We have noted the mobile and desktop projects in constants.py.
https://github.com/mozilla-mobile/testops-dashboard/blob/master/constants.py#L24

Sentry has adopted a somewhat different organization to the projects. In particular there are 3 distinct Fenix-related project in Sentry: fenix, fenix-beta, fenix-nightly. For now I set some constants just for the Sentry related work.
https://github.com/mozilla-mobile/testops-dashboard/pull/197/files#r2379516486