[FEATURE] add cache header to vhost and media format cache

__Tasks:__

- [ ] test coverage
- [ ] gather feedback for my changes
- [x] submit changes to the documentation


__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | none
| Fixed tickets | yes https://github.com/sulu-cmf/SuluMediaBundle/pull/100
| BC Breaks     | no
| Doc           |  [VHost](https://github.com/sulu-cmf/docs/blob/master/developer-documentation/000-foundation/vhost.md), [Cache Headers](/sulu-cmf/docs/blob/master/detail-specification/500-assets/DET-509-Cache-Headers.md)