HealthEndpointAutoConfigurationTests should not rely on CloudFoundry

[snicoll]

We have a few tests that rely on the behavior of a EndpointExposureOutcomeContributor contribution. We do have one for CloudFoundry so we're reusing that behavior.

However, this leads to a few tests to expose cloudfoundry concerns where they shouldn't, really.

[nosan]

I've prepared two branches for this issue:

The first one is pretty straightforward. It is based on CustomEndpointExposureOutcomeContributor, which is registered via test/resources/META-INF/spring.factories.

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The second one also uses CustomEndpointExposureOutcomeContributor, but it is registered with @WithResource. However, it requires additional changes to OnAvailableEndpointCondition, such as passing ConditionContext.getClassLoader() as a parameter to SpringFactoriesLoader.forDefaultResourceLocation().