Only read config if container is initialized

Otherwise fall back to event handler constructor.

The only time (I know of) that the container isn't initialized in .module is during an updb, but by putting the configuration initialization in the earliest event in the lifecycle we can get something close to that after the container is initialized.

Since the event isn't actually dispatched in updb, but the listener IS instantiated, I throw the settings in the constructor to get roughly the same effect.

Closes #3504101