Include PaymentId in payer metadata

Include PaymentId in payer metadata

When receiving a BOLT 12 invoice originating from either an invoice
request or a refund, the invoice should only be paid once. To accomplish
this, require that the invoice includes an encrypted payment id in the
payer metadata. This allows ChannelManager to track a payment when
requesting but prior to receiving the invoice. Thus, it can determine if
the invoice has already been paid.