taprpc: whitelist FetchSupplyLeaves RPC if public read access is enabled

Allow the FetchSupplyLeaves RPC endpoint to be queried without
authentication when the universe server is configured for public read
access. This aligns its access behavior with the FetchSupplyCommit RPC
endpoint.

Author: ffranr

taprpc/perms.go

@@ -375,6 +375,7 @@ func MacaroonWhitelist(allowUniPublicAccessRead bool,
 	if allowUniPublicAccessRead || allowPublicUniProofCourier {
 		whitelist["/universerpc.Universe/QueryProof"] = struct{}{}
 		whitelist["/universerpc.Universe/FetchSupplyCommit"] = struct{}{}
+		whitelist["/universerpc.Universe/FetchSupplyLeaves"] = struct{}{}
 		whitelist["/authmailboxrpc.Mailbox/ReceiveMessages"] = struct{}{}
 	}