No translation files for appdata

### What Happened?

There are no translation files (nor `.pot` and `.po`) in the `po/extra` directory in the project:

### Steps to Reproduce

See https://github.com/elementary/wingpanel-indicator-privacy/tree/master/po/extra

### Expected Behavior

We should generate .pot and .po files in the `po/extra` directory

### OS Version

6.x (Odin)

### Software Version

Compiled from git

### Log Output

```shell
N/A
```

### Hardware Info

N/A

Start by inspecting the po/extra directory and the project's existing translation-generation setup. Confirm how appdata translations are generated, then ensure the expected .pot and .po files are produced in po/extra and verify the directory matches the expected behavior.

Written by the indexing model from the issue text.