We were getting weird errors around the service not calling
startForeground() that I couldn't reproduce. I figure it must be
something with how we only sometimes start the FcmFetchService in the
foreground. So I think the safest thing to do is to just use
GenericForegroundService.
Right now, the only condition is once every 3 minutes on Android 12.
This is ok because Android 12 will allow us (once every 2 minutes or
so) to start a foreground service, and it won't show it for the first 10
seconds. So we can kind of do it without any visual penalty.
Some devices are overzealous with battery management and disallow
starting services even when they're in response to a high-priority FCM
message (which should be allowed). So in these situations, we just
fall back to what we were doing before.
