Purpose
=======
This commit is used to merge 2 models into 1: `slide.slide.resource`
and `slide.slide.link`
Specifications
==============
These models are merged in order to create a unique table for the
*Additional Resources* of a Content.
In order to do that, we merged the models into `slide.slide.resource`
that will contain either a link or a file.
task-2597345
See odoo/enterprise#20480
See odoo/upgrade#2784
Part-of: odoo/odoo#75646
