Previously, when the Jersey-based Actuator was configure with a
separate management port, the resulting child context would fail to
start due to their being no ResourceConfigCustomizer beans available.

This commit updates the configuration so that the customizer's are
injected using an ObjectProvider and an empty list is used in the
event of their being no customizer beans. This aligns the child
context configuration class with JerseyAutoConfiguration which
already used this approach.

Closes gh-12975