Add multi-language OpenAPI specification

I need multi-language API documentation. For now possible to generate single language only (which use in resource files).
How better to implement it? Build instance of `ApiPlatform\OpenApi\OpenApi` with already translated field or do translation during normalization in `ApiPlatform\OpenApi\Serializer\ApiGatewayNormalizer`?

I think better to translate OpenApi instance and propose to implement `OpenApiFactoryInterface` decorator in follow way:

```
// OpenApiTranslator.php

decorated)($context);
return $this->translator->translate($openApi, $lang);
}
}
```

and fix commad `api:openapi:export` command to check which translation available (or add some argument) and generate translated OpenAPI specifications with some suffix in the filename, e.g. 'openapi_en.json', 'openapi_de.json' and etc.