chore: add migration for tracking connected downstream edge nodes (#10765)

https://linear.app/unleash/issue/2-3938/endpoint-in-unleash-edge-validate-license

Database migration for a new `edge_node_presence` table and
`bucket_edge_heartbeat` function.

src/migrations/20251009132935-add-edge-node-presence.js

@@ -0,0 +1,34 @@
+exports.up = function(db, cb) {
+    db.runSql(
+        `
+          CREATE OR REPLACE FUNCTION bucket_edge_heartbeat(ts timestamptz)
+          RETURNS timestamptz
+          LANGUAGE SQL IMMUTABLE PARALLEL SAFE AS $$
+            SELECT to_timestamp(floor(extract(epoch FROM ts) / 300) * 300) AT TIME ZONE 'UTC';
+          $$;
+
+          CREATE TABLE edge_node_presence (
+            bucket_ts     timestamptz NOT NULL,
+            node_ephem_id text        NOT NULL,
+            PRIMARY KEY (bucket_ts, node_ephem_id)
+          );
+
+          CREATE INDEX edge_node_presence_brin ON edge_node_presence USING BRIN (bucket_ts);
+          CREATE INDEX edge_node_presence_node_hash ON edge_node_presence USING HASH (node_ephem_id);
+
+        `,
+        cb,
+    );
+};
+
+exports.down = function(db, cb) {
+    db.runSql(
+        `
+          DROP INDEX IF EXISTS edge_node_presence_brin;
+          DROP INDEX IF EXISTS edge_node_presence_node_hash;
+          DROP TABLE IF EXISTS edge_node_presence;
+          DROP FUNCTION IF EXISTS bucket_edge_heartbeat(timestamptz);
+        `,
+        cb,
+    );
+};