[demo] in-process multinode demonstration

[ellemouton]

Demonstrate in-process graph sharing between LND nodes

This PR adds a multinode binary that can be used to test this LND PR.

The binary starts 2 LND nodes: the graph node and the zane node. Zane will depend on Graph for its remote graph source.

This is how I start the binary on regtest. The flags here are used for the Zane node (note the gossip.no-sync option. The flags for the graph node are specified in the cmd/multinode/main.go file.

function start_graph() {
   cd $LND_DIR
   make tags="dev graphrpc chainrpc peersrpc walletrpc signrpc invoicesrpc autopilotrpc watchtowerrpc wtclientrpc monitoring routerrpc kvdb_postgres kvdb_sqlite"

   ./multinode-debug --bitcoin.regtest \
   --lnddir=$HOME/.lnd-dev-zane --bitcoind.rpchost=localhost:18443 \
   --bitcoin.node=bitcoind \
   --rpclisten=localhost:10019 \
   --bitcoind.rpcuser=lightning --bitcoind.rpcpass=lightning \
   --bitcoind.zmqpubrawblock=tcp://localhost:28332 \
   --bitcoind.zmqpubrawtx=tcp://localhost:28333 \
   --trickledelay=50 \
   --gossip.no-sync \
   --noseedbackup \
   --restlisten=localhost:11019 \
   --rpcmiddleware.enable \
   --listen=localhost:9735 \
   --logging.console.style \
   --bitcoin.active \
   --debuglevel=debug  "$@"
}   

Tests you can perform:

1. Connect Zane to another node in the graph & verify that it only sees itself and the graph node (use lncli describegraph). The graph node should only see itself.
2. Connect zane to another node in the graph & open a private channel with that node.
3. see that zane now sees itself, that channel peer node, and the graph node. It should still not see other things in the graph.
4. now connect the graph node to another peer in the network & wait for it to do gossip sync.
5. now see that zane can see the rest of the network via describegraph BUT that it doesnt actually persist these things (use boltbrowser to confirm)
6. show that zane is able to pay an invoice from a node that it doesnt actually have any persisted info about.

[github-actions]

Pull reviewers stats

Stats of the last 30 days for lnd:

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[coveralls]

Pull Request Test Coverage Report for Build 11774822488

Details

• 1230 of 2738 (44.92%) changed or added relevant lines in 75 files are covered.
• 27897 unchanged lines in 434 files lost coverage.
• Overall coverage decreased (-9.7%) to 49.181%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
chainreg/no_chain_backend.go	0	1	0.0%
chanbackup/pubsub.go	3	4	75.0%
chanbackup/recover.go	3	4	75.0%
chanrestore.go	5	6	83.33%
lnrpc/devrpc/dev_server.go	0	1	0.0%
lnrpc/devrpc/driver.go	0	1	0.0%
lnrpc/routerrpc/router_backend.go	0	1	0.0%
routing/graph.go	3	4	75.0%
routing/localchans/manager.go	4	5	80.0%
routing/router.go	10	11	90.91%

Files with Coverage Reduction	New Missed Lines	%
graph/errors.go	1	94.74%
lnwire/typed_lease_expiry.go	2	78.95%
lnwire/typed_fee.go	2	66.67%
htlcswitch/linkfailure.go	2	58.62%
routing/graph.go	2	86.96%
channeldb/forwarding_policy.go	2	85.14%
record/hop.go	2	93.33%
rpcperms/interceptor.go	2	82.59%
lnwire/short_channel_id.go	2	89.74%
lnwallet/sigpool.go	2	65.63%

Totals
Change from base Build 11739445466:	-9.7%
Covered Lines:	99114
Relevant Lines:	201531

---

💛 - Coveralls