sqldb+graph/db: source nodes table, queries and CRUD

In this commit, we add the `source_nodes` table. It points to entries in
the `nodes` table. This table will store one entry per protocol version
that we are announcing a node_announcement on.

With this commit, we can run the TestSourceNode unit test against our
SQL backends.

sqldb/sqlc/migrations/000007_graph.down.sql

@@ -3,8 +3,10 @@ DROP INDEX IF EXISTS nodes_unique;
 DROP INDEX IF EXISTS node_extra_types_unique;
 DROP INDEX IF EXISTS node_features_unique;
 DROP INDEX IF EXISTS node_addresses_unique;
+DROP INDEX IF EXISTS source_nodes_unique;
 
 -- Drop tables in order of reverse dependencies.
+DROP TABLE IF EXISTS source_nodes;
 DROP TABLE IF EXISTS node_addresses;
 DROP TABLE IF EXISTS node_features;
 DROP TABLE IF EXISTS node_extra_types;

sqldb/sqlc/migrations/000007_graph.up.sql

@@ -87,4 +87,11 @@ CREATE TABLE IF NOT EXISTS node_addresses (
 );
 CREATE UNIQUE INDEX IF NOT EXISTS node_addresses_unique ON node_addresses (
     node_id, type, position
+);
+
+CREATE TABLE IF NOT EXISTS source_nodes (
+    node_id BIGINT NOT NULL REFERENCES nodes (id) ON DELETE CASCADE
+);
+CREATE UNIQUE INDEX IF NOT EXISTS source_nodes_unique ON source_nodes (
+    node_id
 );