Add a `documentation_formats` that differs from `formats`

[jdeniau]

If you de-activate the json format from the configuration, you can not use like ReDoc. You can not use the integrated swagger if you disable html format.

Personally, I disable everything except json-ld (less options means less bugs ;) ).

Furthermore, I don't think that enabling html format is really pertinent for an API, but it does for the documentation.

Do you think it's a good idea to split formats from the documentation_formats, this way, we could do something like:

api_platform:
    formats: 
        jsonld: ['application/ld+json']
    documentation_formats: 
        html: ['text/html']
        json: ['application/json']

As usual, I will open a PR if you agree with this.

[Simperfit]

I think this can be implemented ? Do you have time to contribute it ?

Thanks!

[jdeniau]

Yes I can.
Will do if you think it's a good idea