[16.0][FIX] fs_attachment: Fix attachment store after upgrade

[lmignon]

Fix attachments stored in Odoo after an addon upgrade.

Prerequisites:

• The fs_attachment addon is installed, and specific filesystem storage is configured.
• All the attachments are already stored in the appropriate filesystem storage. (We assume that if you've installed the addon on an existing database, you'vealready migrated the existing attachments appropriately.

Context:

• You run an upgrade command on your Odoo server.

Problem:

Some attachments could be created during the upgrade process before the load of the fs_attachment module or the configuration of the filesystem storage backends. This is especially true for the attachments created by addons to store the app icons or even attachments from XML data files. As a result, you end up with attachments that could not be found by some Odoo instances if, for example, you have multiple Odoo instances running on different servers since these attachments are stored in the odoo filestore of the server that created them.

Solution:

A solution to this problem is to hook the end of the upgrade process through the implementation of the _register_hook method on our ir.attachment model. Since this method is called after the completion of the upgrade process and the full initialization of the odoo registry, we can safely expect that all the information we need to know where to store the attachments are available. From there, we can simply search for all the attachments that are not linked to any specific storage and store them in the appropriate storage.

[lmignon]

cc @sbidoul @adrienpeiffer

[CasVissers-360ERP]

@lmignon @sbidoul are you aware that the base vacuuming of Odoo will never run, also for the ignored files?

https://github.com/odoo/odoo/blob/e721ed146d6173cc04efe6103aa6e682fb62917f/odoo/addons/base/models/ir_attachment.py#L165

[CasVissers-360ERP]

In addition I think there is an issue with force_storage #310