Refactor several areas of the actuator endpoint code in order to make
future extensions easier. The primary goal is to introduce the concept
of an `ExposableEndpoint` that has technology specific subclasses and
can carry additional data for filters to use. Many other changes have
been made along the way including:

* A new EndpointSupplier interface that allows cleaner separation of
  supplying vs discovering endpoints. This allows cleaner class names
  and allows for better auto-configuration since a user can choose to
  provide their own supplier entirely.

* A `DiscoveredEndpoint` interface that allows the `EndpointFilter`
  to be greatly simplified. A filter now doesn't need to know about
  discovery concerns unless absolutely necessary.

* Improved naming and package structure. Many technology specific
  concerns are now grouped in a better way. Related concerns are
  co-located and concepts from one area no longer leakage into another.

* Simplified `HandlerMapping` implementations. Many common concerns have
  been pulled up helping to create simpler subclasses.

* Simplified JMX adapters. Many of the intermediary `Info` classes have
  been removed. The `DiscoveredJmxOperation` is now responsible for
  mapping methods to operations.

* A specific @`HealthEndpointCloudFoundryExtension` for Cloud Foundry.
  The extension logic used to create a "full" health endpoint extension
  has been made explicit.

Fixes gh-11428
Fixes gh-11581