peer+lnd: add new CLI option to control if we D/C on slow pongs

In this commit, we add a new CLI option to control if we D/C on slow
pongs or not. Due to the existence of head-of-the-line blocking at
various levels of abstraction (app buffer, slow processing, TCP kernel
buffers, etc), if there's a flurry of gossip messages (eg: 1K channel
updates), then even with a reasonable processing latency, a peer may
still not read our ping in time.

To give users another option, we add a flag that allows users to disable
this behavior. The default remains.

server.go

@@ -4493,6 +4493,7 @@ func (s *server) peerConnected(conn net.Conn, connReq *connmgr.ConnReq,
 				EndorsementExperimentEnd,
 			)
 		},
+		NoDisconnectOnPongFailure: s.cfg.NoDisconnectOnPongFailure,
 	}
 
 	copy(pCfg.PubKeyBytes[:], peerAddr.IdentityKey.SerializeCompressed())