Adding robots.txt override via admin control panel

This is a requested low priority feature in #418 - I created the changes
to follow similarly to how the Instance Description is handled.

packages/backend/migration/1738098171990-robotsTxt.js

@@ -0,0 +1,16 @@
+/*
+ * SPDX-FileCopyrightText: marie and other Sharkey contributors
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+export class RobotsTxt1738098171990 {
+    name = 'RobotsTxt1738098171990'
+
+    async up(queryRunner) {
+        await queryRunner.query(`ALTER TABLE "meta" ADD "robotsTxt" character varying(2048)`);
+    }
+
+    async down(queryRunner) {
+        await queryRunner.query(`ALTER TABLE "meta" DROP COLUMN "robotsTxt"`);
+    }
+}