OpenCitations - content-negotiation

hi Silvio 

@essepuntato 

RoHub implemented content negotiation 

```
    curl --location --request GET 'https://w3id.org/ro-id/ce91c342-9009-4f7a-bfec-1358368feda7' --header 'Accept: application/vnd.skgif.ld+json'​
```

we discussed the content-negotiation name here https://github.com/skg-if/api/issues/6 

Do you think we could have content negotiation for OpenCitations as well ?
