This will prevent the subservers from writing macaroons to disk
when the stateless_init flag is set to true. It accomplishes
this by storing the StatelessInit value in the Macaroon Service.
Previously it wasn't possible to store a preimage in the invoice
database and signal that a payment should not be settled right away. The
only way to hold a payment was to insert the magic UnknownPreimage value
in the invoice database. This commit introduces a distinct flag to
signal that an invoice is a hold invoice and thereby allows the preimage
to be present in the database already.
Preparation for (key send) hodl invoices for which we already know the
preimage.
In this commit, we remove the restriction surrounding the largest
invoices that we'll allow a user to create. After #3967 has landed,
users will be able to send in _aggregate_ a payment larger than the
current max HTLC size limit in the network. As a result, we can just
treat that value as the system's MTU, and allow users to request
payments it multiples of that MTU value.
A follow up to this PR at a later time will also allow wumbo _channels_.
However, that requires us to tweak the way we scale CSV values, as post
wumbo, there is no true channel size limit, only the
_local_ limit of a given node. We also need to implement a way for nodes
to signal to other nodes their accepted max channel size.
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.
