Changes to Get futures curve structure

the response property data/back_month_6 became nullable for the status 200

the response property data/severity became nullable for the status 200

the data/curve_points response's property type changed from array to integer for status 200

added the optional property data/caveat to the response with the 200 status

added the optional property data/methodology to the response with the 200 status

added the optional property data/seasonally_adjusted to the response with the 200 status

added the optional property data/spread_tenors_months to the response with the 200 status

added the optional property data/term_slope_pct to the response with the 200 status

added the optional property data/warnings to the response with the 200 status

added the new required query request parameter commodity

added the media type application/json for the response with the status 200

added the media type application/json for the response with the status 401

added the non-success response with the status 400

added the non-success response with the status 500