Submits an Enrollment for the given Program.
Any Enrollment created via this path requires vendor approval, and so
will begin with the status pendingvendor.
When using the pairingcode flow, clients can avoid duplicate submissions using
the specified Idempotency-Key header. Appropriate values are non-PII customer
identifiers which guarantee a unique customer on the clients' end. Neither
the deviceIdentifier nor the utilityAccountNumber fields are allowed in this flow.
When using the preapproved flow, the Idempotency-Key header is ignored.
The deviceIdentifier and utilityAccountNumber fields in combination obviate the
need for it in this flow. The deviceIdentifier field is required in this flow,
and the utilityAccountNumber field is optional.
