[Xamarin] RealmTasks should allow install alongside others

[AndyDentFree]

The Xamarin versions for iOS and Android should have a unique signature to allow installation alongside the existing apps.

I suggest we change the final s to x ie io.realm.realmtaskx

[nirinchev]

I was thinking about io.realm.realmtasx, but @fealebenpae hated it 😿 We could also spell it out completely - io.realm.tasks-xamarin.

[jpsim]

please don't butcher the app name in the id for no reason. We use io.realm.realmtasks.ios and io.realm.realmtasks.macos so far, might as well use io.realm.realmtasks.xamarin.

[nirinchev]

io.realm.realmtasks.xamarin it is.