RDF convertors should not read or write plain JSON

As discovered by @joepio in https://github.com/CommunitySolidServer/CommunitySolidServer/issues/275

Terminal 1

git checkout 3c32466d8873e73328f678acce1260fea02cabc9 # latest main
npm ci
npm start

Terminal 2

echo '{}' | curl -T - -H "Content-Type: application/json" http://localhost:3000/test
curl -H "Accept: text/turtle" http://localhost:3000/test

Log

2022-03-28T20:27:59.225Z [BaseHttpServerFactory] info: Received GET request for /test
2022-03-28T20:27:59.241Z [WebAclReader] info: Reading ACL statements from http://localhost:3000/.acl
2022-03-28T20:27:59.249Z [StreamUtil] warn: Piped stream errored with Missing context link header for media type application/json on http://localhost:3000/test
2022-03-28T20:27:59.250Z [StreamUtil] warn: Piped stream errored with Missing context link header for media type application/json on http://localhost:3000/test
2022-03-28T20:27:59.252Z [StreamUtil] warn: Piped stream errored with Missing context link header for media type application/json on http://localhost:3000/test
2022-03-28T20:27:59.252Z [BasicResponseWriter] error: Writing to HttpResponse failed with message Missing context link header for media type application/json on http://localhost:3000/test
2022-03-28T20:28:00.255Z [GuardedStream] error: No error listener was attached but error was thrown: aborted

Expected

200 or 406

[joachimvh]

That is going to require a MetadataParser that instead of putting header data into metadata throws an error if it sees a context header (specifically with application/json content type perhaps).

[joachimvh]

Done in #1359