feat: message banners table migration (#5009)

https://linear.app/unleash/issue/2-1485/db-create-migration-for-a-new-internal-message-banners-table

Adds a DB migration for a new `message_banners` table.

src/migrations/20231012082537-message-banners.js

@@ -0,0 +1,32 @@
+'use strict';
+
+exports.up = function (db, cb) {
+    db.runSql(
+        `
+        CREATE TABLE IF NOT EXISTS message_banners
+            (
+                id SERIAL PRIMARY KEY NOT NULL,
+                enabled BOOLEAN DEFAULT true NOT NULL,
+                message TEXT NOT NULL,
+                variant TEXT,
+                sticky BOOLEAN DEFAULT false,
+                icon TEXT,
+                link TEXT,
+                link_text TEXT,
+                dialog_title TEXT,
+                dialog TEXT,
+                created_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT now()
+            );
+        `,
+        cb,
+    );
+};
+
+exports.down = function (db, cb) {
+    db.runSql(
+        `
+        DROP TABLE IF EXISTS message_banners;
+        `,
+        cb,
+    );
+};