Rename artifacts/package

Follow Spring starter naming conventions

at the moment artifacts are named opentracing-spring-cloud-<module>-starter, however spring uses convention spring-boot-starter-<module>

https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#using-boot-starter
Although it's spring convention, the docs shows an example like acme-spring-boot-starter.

Rename from opentracing-spring-cloud to something else

This project is a collection of instrumentation for Spring Boot. Spring Cloud seems to be as a subset to spring boot. It anyways depends on SB.

I have a couple of proposals:

1. opentracing-spring-boot- this is my preferred
2. opentracing-spring-k

The rename will break users - groupId but also we should change package and configuration https://github.com/opentracing-contrib/java-spring-cloud/blob/master/instrument-starters/opentracing-spring-cloud-core/src/main/resources/META-INF/additional-spring-configuration-metadata.json#L4

Start by inventorying artifacts under instrument-starters, including opentracing-spring-cloud-core, and inspect additional-spring-configuration-metadata.json. Review the Spring Boot starter naming guidance and determine the complete impact on artifact names, groupId, packages, and configuration; done means the naming is consistently migrated with the breaking changes accounted for.