lncfg: add new PrunedNodeMaxPeers config option/flag

sample-lnd.conf

@@ -536,6 +536,10 @@ bitcoin.node=btcd
 ; If unset, the default value is "CONSERVATIVE".
 ; bitcoind.estimatemode=CONSERVATIVE
 
+; The maximum number of peers lnd will choose from the backend node to retrieve
+; pruned blocks from. This only applies to pruned nodes.
+; bitcoind.pruned-node-max-peers=4
+
 [neutrino]
 
 ; Connect only to the specified peers at startup. This creates a persistent
@@ -706,6 +710,10 @@ litecoin.node=ltcd
 ; If unset, the default value is "CONSERVATIVE".
 ; litecoind.estimatemode=CONSERVATIVE
 
+; The maximum number of peers lnd will choose from the backend node to retrieve
+; pruned blocks from. This only applies to pruned nodes.
+; litecoind.pruned-node-max-peers=4
+
 [autopilot]
 
 ; If the autopilot agent should be active or not. The autopilot agent will