This change updates the stripecoinpayments service to optionally skip
generating line items for payments records that have no egress, storage,
or segments for the billing period.
This results in a reduction from 4 to 1 Stripe API calls for customers
who have no usage. The final API call is the attempt to generate an
invoice on stripe, which expectedly fails because there are no unapplied line
items. Removing that final API call would require some additional
queries and is out of scope for this change.
This functionality is behind the
`payments.stripe-coin-payments.skip-empty-invoices` feature flag.
https://github.com/storj/storj/issues/5381
Change-Id: Id184969a4c79047c40502336d69c51388ab03bf8
99206fca04