graph/db+sqldb: impl IsPublicNode

Which lets us run `TestNodeIsPublic` against our SQL DB backends.
Note that we need to tweak the tests a little bit so that
`AddLightningNode` for the same node is always called with a newer
LastUpdate time else it will fail the SQL constraint that only allows
the upsert if the update is newer than the persisted one.

sqldb/sqlc/queries/graph.sql

@@ -47,6 +47,24 @@ WHERE version = $1  AND id > $2
 ORDER BY id
 LIMIT $3;
 
+-- name: IsPublicV1Node :one
+SELECT EXISTS (
+    SELECT 1
+    FROM channels c
+    JOIN nodes n ON n.id = c.node_id_1 OR n.id = c.node_id_2
+    -- NOTE: we hard-code the version here since the clauses
+    -- here that determine if a node is public is specific
+    -- to the V1 gossip protocol. In V1, a node is public
+    -- if it has a public channel and a public channel is one
+    -- where we have the set of signatures of the channel
+    -- announcement. It is enough to just check that we have
+    -- one of the signatures since we only ever set them
+    -- together.
+    WHERE c.version = 1
+      AND c.bitcoin_1_signature IS NOT NULL
+      AND n.pub_key = $1
+);
+
 -- name: DeleteNodeByPubKey :execresult
 DELETE FROM nodes
 WHERE pub_key = $1