Set Fenix Version Name in build

By default, the app versionName is not set. Fennec uses the Firefox version name as the versionName.

Mozilla releases Nightly with the name Nightly $date $time (where date is YYYYMMDD, and time is HH:MM). See

https://gitlab.torproject.org/tpo/applications/fenix/-/blob/tor-browser-80.0b6-10-1/taskcluster/fenix_taskgraph/transforms/build.py#L85

and some "version" config for beta/release:

https://gitlab.torproject.org/tpo/applications/fenix/-/blob/tor-browser-80.0b6-10-1/taskcluster/fenix_taskgraph/transforms/build.py#L98

I think they're just using the Fenix git tag (without the leading v) as the name (the current Firefox Beta has the versionName as 80.0.1-beta.2).