Add an event that indicates the Spring Application has fully started and
is now ready to service requests. While ContextRefreshEvent provides
such hook for a regular spring application, this dedicated event is
triggered once all callbacks have been processed and right before the
context is returned to the caller. Besides, such event is triggered once
per application, regardless of the number of (child) contexts that could
have been created.
Closes gh-2638
7b2b11903a