build: extend sample-lnd-conf with db.etcd.embedded

sample-lnd.conf

@@ -952,6 +952,10 @@ litecoin.node=ltcd
 ; Whether to collect etcd commit stats.
 ; db.etcd.collect_stats=true
 
+; If set LND will use an embedded etcd instance instead of the external one.
+; Useful for testing.
+; db.etcd.embedded=false
+
 [bolt]
 ; If true, prevents the database from syncing its freelist to disk. 
 ; db.bolt.nofreelistsync=1