Changes to Create a billable metric

the response property billable_metric/description became required for the status 200

the response property billable_metric/expression became required for the status 200

the response property billable_metric/field_name became required for the status 200

the response property billable_metric/rounding_function became required for the status 200

the response property billable_metric/rounding_precision became required for the status 200

the response property billable_metric/weighted_interval became required for the status 200

the response property billable_metric/expression became nullable for the status 200

the response property billable_metric/filters became required for the status 200