Feedback of ignored values in POST requests

[dmlls]

Right now, if the API receives an attribute that is not expected, e.g. "linguistic_register", it will simply ignore it. However, the user receives no feedback of this. The only way they can now is by checking the summarization parameters returned in the API response.

Expected feature: implement feedback of ignored attributes in POST calls. This feedback should contain the reason why a certain attribute was ignored, e.g.:

• "The attribute 'linguistic_register' is not recognized. It will be ignored.", or
• "The attribute 'relative_min_length' takes float values between 0.0 and 1.0. Value provided: 66.6. A default value will be used.".