In this commit, we add a new `LookupInvoiceV2` method attached to the
invoice RPC sub-server. Compared to the existing version, this version
allows an invoice to be looked up by an invoice ref. This enables users
to query an AMP invoice based on a specific _set ID_, so they can get
the information related to the set of cumulative settles to that
invoices.
To avoid a naming conflict with etcd, we rename our very generic
rpc.proto to lightning.proto to match the service name that's declared
within. This will break many external tutorials and possibly also our
API docs but the change needs to be done eventually.
We now use the jsonpb marshaler to convert the RPC responses to
JSON in lncli and REST. The jsonpb has a setting to use the
original name as defined in the proto file and the explicit
json_name definition is not necessary any more.
The jsonpb setting is called OrigName and needs to be true.
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.
