Provide variants of `WebClient` and `WebConnectionHtmlUnitDriver` that
automatically resolve relative URLs to "localhost:${local.server.port}".
Fixes gh-5472
Add a `@MockBean` annotation which can be used to setup and inject mocks
into an application context. The annotation can be used on test classes,
test fields, configuration classes or configuration fields. When used on
a field the annotation also acts as an injection point.
Fixes gh-5042
