Update `TestcontainersLifecycleBeanPostProcessor` so that containers
are now initialized either on the first `postProcessAfterInitialization`
call with a frozen configuration or just before a test container
property is supplied.
Prior to this commit, it was assumed that the first post-process call
after the configuration was frozen was suitably early to initialize
the containers. This turns out to not be no always the case.
Specifically, in the `finishBeanFactoryInitialization` method of
`AbstractApplicationContext` we see that `LoadTimeWeaverAware` beans
are obtained before the configuration is frozen. One such bean is
`DefaultPersistenceUnitManager` which is likely to need datasource
properties that will require a started container.
To fix the problem, the `TestcontainersPropertySource` now publishes
a `BeforeTestcontainersPropertySuppliedEvent` to the ApplicationContext
just before any value is supplied. By listening for this event, we can
ensure that containers are initialized and started before any dynamic
property is read.
Fixes gh-38913
89874d351a