Support for configuring an endpoint’s path separately from its id was
introduced in 97255785, but it didn’t work for a variety of reasons:

 1. Some custom MVC endpoints did not have configuration properties
    bound to them
 2. Some generic endpoints rejected the path property as they were
    configured not to ignore unknown fields
 3. The property used to configure the path was dependent on the id
    of the endpoint. This meant that the path property’s name would
    change if the endpoint’s id was changed

This commit addresses these problems:

 1. @ConfigurationProperties has been added to custom MvcEndpoints where
    it was missing
 2. Generic endpoints have been updated to ignore unknown fields,
    allowing the path of their MVC adapter to be configured
 3. Rather than using the id of a generic endpoint to determine the name
    of its path property, the prefix or value of the endpoint’s
    @ConfigurationProperties annotation is used instead. Any generic
    endpoint that is not annotated with @ConfigurationProperties is
    ignored, making its path unconfigurable.

Closes gh-5105