Implemented file tokens for bulky items

[Toflar]

This implements a general listener for all bulky items.

For example, if you have a ##form_upload## field with an associated bulky items voucher, you will now automatically also get a ##file_item_html_form_upload## and ##file_item_text_form_upload## token.
You notice, the format is: file_item_<format>_<tokenName>.

The contents of those are defined by the new @Contao/notification_center/file_token.html.twig template which you can adjust. By default it will generate the following outputs:

For text:

- [test.png (10,9 KiB)](https://example.com/notifications/download/20241119/58161a5d-9e87-4fc8-839b-5ccfb1fa2aca?_hash=foobar)
- [test__2.png (10,9 KiB)](https://example.com/notifications/download/20241119/654bd791-3ff7-4480-8f75-801387178d16?_hash=foobar)

For html:

<ul>
  <li><a href="https://example.com/notifications/download/20241119/58161a5d-9e87-4fc8-839b-5ccfb1fa2aca?_hash=foobar">test.png (10,9 KiB)</a></li>
  <li><a href="https://example.com/notifications/download/20241119/654bd791-3ff7-4480-8f75-801387178d16?_hash=foobar">test__2.png (10,9 KiB)</a></li>
</ul>

You may adjust the @Contao/notification_center/file_token.html.twig according to your needs. You get the file items, the format but also the entire Parcel as template context in case you need to do anything complex.

The Twig template uses a notification_center_file_url() method that generates the URL to the file. It takes an optional 2nd parameter for $ttl in case you want to limit the downloads to a certain expiry date which I don't think is a requirement by default.