Added migration to update group for new portal settings

closes https://github.com/TryGhost/Ghost/issues/12026

- 3 new portal settings were added in `3.23` in default settings - `portal_button_style`, `portal_button_icon`, `portal_button_signup_text`
- New settings default to group `core` on migrating from pre 3.22 versions due to missing columns in DB
- Migration here updates the new settings to correct group

core/server/data/migrations/versions/3.24/01-populate-group-for-new-portal-settings.js

@@ -0,0 +1,37 @@
+const logging = require('../../../../../shared/logging');
+
+// new setting keys and group mapping
+const groupMapping = [{
+    group: 'portal',
+    keys: [
+        'portal_button_style',
+        'portal_button_icon',
+        'portal_button_signup_text'
+    ]
+}];
+
+module.exports = {
+    config: {
+        transaction: true
+    },
+
+    async up(options) {
+        // set the correct group value for new settings
+        await Promise.map(groupMapping, async (groupMap) => {
+            return await Promise.map(groupMap.keys, async (key) => {
+                logging.info(`Updating setting ${key} to group ${groupMap.group}`);
+
+                return await options
+                    .transacting('settings')
+                    .where('key', key)
+                    .update({
+                        group: groupMap.group
+                    });
+            });
+        });
+    },
+
+    // `up` is only run to update correct group value for each setting instead of default.
+    // it doesn't make sense to be revert a setting's group to default `core` again
+    async down() {}
+};