This commit changes the way of populating the default
job registry from using a BeanPostProcessor to using
a JobRegistrySmartInitializingSingleton. This change
resolves warnings about beans being eagerly injected
into currently created BeanPostProcessors and prevents
lifecycle issues about early bean initializations.
It also deprecates JobRegistryBeanPostProcessor in favor
of JobRegistrySmartInitializingSingleton.
Resolves#4547
