[feature]: Make sure LND re-sends AnnouncementSignature after disconnect.

Make sure LND always re-sends the AnnouncmentSignature in case the Peer disconnects before receiving it the first time.

@t-bast not sure if I understood the requirement correctly, when can we assume that the peer received the Signature ? Can we assume it at one point ?

came up in https://github.com/lightning/bolts/issues/1258