Add Zipkin to zero-config services

[odrotbohm]

It would be nice if a Zipkin instance could be provisioned if the io.zipkin.zipkin2:zipkin dependency is on the classpath. This is a dependency commonly depended on if you're using Spring Boot's new observability features.

[maciejwalkowiak]

Thanks for an idea @odrotbohm! Will be included in the next release