Add a step to check if all elements from the BOM resolve

[marcingrzejszczak]

Recent example with Sleuth. For 3.0.0-M5 I removed the spring-cloud-starter-zipkin however I've forgotten to remove it from the BOM. We could try to resolve each of the entries from the BOM (e.g. org.springframework.cloud:spring-cloud-starter-zipkin:3.0.0-M5 would fail).