Embedded image upload broken

[btry]

Image uploads in textarea is hacky and broke, ~probably due to switching to unsigned int IDs and FK.~

This PR solved the problem by converting uploads as documents immediately, contrary to previous implemntation. To handle generation of tickets the uploaded stream is re-used to simulate an upload, like it is currently implemented for questions of type file.

When showing a form answer from simplified interface, documents are not accessible. We need to provide itemtype and items_id identifiers to an object linked to the document, and viewable by the curent user. (see https://github.com/glpi-project/glpi/pull/10945 ). Formcreator cannot rely on GLPI to build such URL for now.

Needs an improvement to avoid a duplicate of its code in the plugin.