Add reference application for new Getting Started

[svrnm]

Hey there,

after a few months of silence I finally got back to the project for a new getting started app. I merged the specification for the reference app into the oteldotio repo, and now I am looking for language SIGs that go ahead and implement it:

• https://opentelemetry.io/docs/getting-started/reference-application-specification/
• https://github.com/open-telemetry/opentelemetry.io/blob/main/content/en/docs/getting-started/reference-application-specification.md

With this dedicated examples repository, I think java is a good language to start with!

Thanks:-)