data_connector: schema.json, adding description attribute for field definition?

[peiwangdb]

Adding a description for the parameters will help the users understand how to specify values for each parameter. For example, the format of the longitude in Yelp.businesses table; the maximum limit of the results that a user can expect (if we incorporate limit parameter in the future).

[dovahcrow]

@peiwangdb you can change the dataprep.connector.schema.defs.FieldDef for this purpose.