SpringBoot Enforce that builder and run images are pulled from the same authenticated registry

When the Gradle bootBuildImage task or Maven spring-boot:build-image goal is configured with an authenticated registry using docker.builderRegistry, both the builder image and run image will be pulled using the same registry credentials. The plugins should validate that both images are specified with a registry matching the registry specified in docker.builderRegistry and throw an obvious error message if that's not the case.

Comment From: scottfrederick

both images are specified with a registry matching the registry specified in docker.builderRegistry

On further analysis, we should just verify that the builder and run images are in the same registry when docker.builderRegistry authentication is configured. With user authentication, docker.builderRegistry.url is an optional field (only docker.builderRegistry.username and docker.builderRegistry.password are required by the registry) and there is no URL provided with token authentication.