Enhancing docs with description on parameters returned in the response

[FabiKo117]

What is missing in the docs is a list of which parameters are to expect to be included in the response and a short explanation of them. This particularly applies to the data-extraction endpoints, where we return information about the time of validity (@validfrom and @validto), the id of the OSM feature in the format of -osmType-/-id-, or for the new /contributions endpoint the information on the type of the contribution (@tagChange, @geometryChange, etc.).

We should also add the info on which parameters are to expect for which request parameters, e.g.:
Which reponse parameters are included when I set properties=metadata in the request?