OpenAPI: Return mastoapi-compliant errors
Currently when OpenAPI validation fails, it returns something like this to the client:
{"errors":[{"message":"Missing field: client_name","source":{"pointer":"/client_name"},"title":"Invalid value"},{"message":"Missing field: redirect_uris","source":{"pointer":"/redirect_uris"},"title":"Invalid value"}]}
Instead a mastoapi-compliant error should be returned, for example:
{"error": "Missing field: redirect_uris. Misssing field: client_name"}
They should also be localised
cc @egor
Edited by rinpatch