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/src/models/json-schema/meta.ts

@@ -139,6 +139,10 @@ export const packedMetaLiteSchema = {
 			type: 'boolean',
 			optional: false, nullable: true,
 		},
+		robotsTxt: {
+			type: 'string',
+			optional: false, nullable: true,
+		},
 		enableTestcaptcha: {
 			type: 'boolean',
 			optional: false, nullable: false,