This commit upgrades the protobuf version. Compared to the previous
v1.2.0 it generates smaller diffs in generated code. This change was
introduced in:
fffb0f7828
This fixes a bug where the RHashStr field on the PaymentHash request for
SubscribeSingleInvoice was being ignored. This replaces the PaymentHash
message for the SubscribeSingleInvoice request with a new message called
SubscribeSingleInvoiceRequest that contains only the RHash field.
This commit modifies the invoice registry to handle invoices for which
the preimage is not known yet (hodl invoices). In that case, the
resolution channel passed in from links and resolvers is stored until we
either learn the preimage or want to cancel the htlc.
