Improve white label errors for concrete tests

[dgarijo]

For example, when doing a GET to https://foops.linkeddata.es/assess/test/OM1 (which is not supported), I see an error page.
Instead, I should be redirected to the API page: https://w3id.org/foops/api.

This method is only supported through a post request at the moment

[juanjemdIos]

Not sure about this. After a GET to https://foops.linkeddata.es/assess/test/OM1 we obtain this:
Please send a POST request. Example:
curl -X POST "https://foops.linkeddata.es/assess/test/OM1" -H "accept: application/json" -H "Content-Type: application/json" -d "{ "resource_identifier": "https://w3id.org/example#\"}"

Redirect to page: https://w3id.org/foops/api open the same https://foops.linkeddata.es/swagger-ui/index.html#/foops-controller again.
But I've made a get for assessOntologyFile because it only had a POST. It was a white label error