Improve trix and action text support

[Paul-Bob]

Feature

Trix field have some limitations:

1. File attachment is possible only on persistent records https://github.com/avo-hq/avo/issues/2713
2. File attachment is possible only whit explicit attachment_key
3. File attachments are corrupt except images on action text. (has_rich_text) https://github.com/avo-hq/avo/issues/2538

Let's explore this possibility:

1. When attachment_key is set that means we need a persistent record with that attachment_key association. So limitation points 1 and 2 still applying.
2. When attachment_key is not set that means the user do not want to associate the attachments to a fixed key/association. We can generate a random key like here https://trix-editor.org/js/attachments.js and in this case the limitation points 1 and 2 will not apply, i.e there is no need for a record and neither attachment_key.