[WIP] Newsletter bundle

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | no
| Fixed tickets | 
| License       | MIT
| Doc PR        | Sylius/Sylius-Docs#218
why references are upper cased, is that similar to other fixtures? just curious maybe we should lock them to lower case