added context tags for services

__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes
- [ ] submit changes to the documentation

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | fixes https://github.com/sulu-cmf/sulu-standard/issues/114
| BC Breaks     | none
| Doc           | https://github.com/sulu-cmf/docs/tree/master/developer-documentation/000-foundation
this should be before retrieving the tagged services