LSPS2: invalid client-side payment size handling

[johncantrell97]

The client specifies the optional payment_size_msat at the start of the flow but we don't learn about the min_payment_size_msat and max_payment_size_msat the LSP supports until we receive the GetInfoResponse. We currently do not check if the provided payment size is within these bounds.

I'm not sure the best way to handle it though. I guess instead of surfacing the GetInfoResponse event to the end-user we would surface some kind of error event?

Thoughts?

[johncantrell97]

Alternatively we could allow the client to continue and issue the buy request which would fail due to the LSP checking the bounds on the payment size.