Previously, @EndpointFilter would only have an effect when used as
an annotation or meta-annotation on the endpoint class itself. It
would have no effect when used on a super-class of the endpoint
bean's class.

This commit updates EndpointDiscoverer so that an @EndpointFilter
annotation or meta-annotation on a super-class will be found and
applied to the discovery process. This is achieved by using find…
rather than get… when retrieving the attributes for the EndpointFilter
annotation.

Fixes gh-17866