Changes to Get a billing limit-increase request

the request/approved_increase_amount response's property pattern was changed from ^([1-9][0-9]*(\.[0-9]+)?|0\.[0-9]*[1-9][0-9]*)$ to ^-?([1-9][0-9]*(\.[0-9]+)?|0\.[0-9]*[1-9][0-9]*)$ for the status 200

endpoint added