sqldb/sqlc: add IsPublicV2Node query

Add SQL query to determine if a node has public v2 channels. Unlike
v1 which requires all four individual signatures, v2 channels are
considered public when the single aggregated signature is present.

sqldb/sqlc/queries/graph.sql

@@ -112,6 +112,28 @@ SELECT EXISTS (
       AND n.pub_key = $1
 );
 
+-- name: IsPublicV2Node :one
+SELECT EXISTS (
+    SELECT 1
+    FROM graph_channels c
+    JOIN graph_nodes n ON n.id = c.node_id_1
+    -- NOTE: we hard-code the version here since the clauses
+    -- here that determine if a node is public is specific
+    -- to the V2 gossip protocol.
+    WHERE c.version = 2
+      AND c.signature IS NOT NULL
+      AND n.pub_key = $1
+
+    UNION ALL
+
+    SELECT 1
+    FROM graph_channels c
+    JOIN graph_nodes n ON n.id = c.node_id_2
+    WHERE c.version = 2
+      AND COALESCE(length(c.signature), 0) > 0
+      AND n.pub_key = $1
+);
+
 -- name: DeleteUnconnectedNodes :many
 DELETE FROM graph_nodes
 WHERE