Changes to List all billable metrics

the response property billable_metrics/items/description became required for the status 200

the response property billable_metrics/items/expression became required for the status 200

the response property billable_metrics/items/field_name became required for the status 200

the response property billable_metrics/items/rounding_function became required for the status 200

the response property billable_metrics/items/rounding_precision became required for the status 200

the response property billable_metrics/items/weighted_interval became required for the status 200

the response property billable_metrics/items/expression became nullable for the status 200

the response property billable_metrics/items/filters became required for the status 200