Gets billed usage for the specified L1 for a given billing month; Usage is shown
only for months for which the bill is generated. It includes details like
bill duration, entity details, metric name, usage, unit, rate, currency and cost.
If query params are not specified, then it will default to 'month={last billed month} and
year={last billed year}'.
Input parameters:
serviceInstanceId - the id of the service instance to which l1 belongs.
l1Id - the id of l1 whose billed usage is to be fetched.
month - the billing month of billed usage.
year - the billing year of billed usage.
/api/billing/service-instance/{serviceInstanceId}/l1/{l1Id}/billed-usage