[Task]: Switch icon/preview upload and resize code to use storage class

[diox]

Description

The icon & preview upload code is extremely old and does a bunch of filesystem operations that are dangerous (renaming and removing files) using python os directly.

For safety and consistency, it should use storage classes instead - using a storage class instantiated with TMP_PATH so that it cannot access files outside of this directory (upload_image() does use storage already but it uses the default storage that starts from STORAGE_ROOT so it doesn't offer that kind of protection).

Affected functions:

• devhub.views.upload_image()
• addons.tasks.resize_preview()
• addons.tasks.resize_icon()

Acceptance Criteria

• devhub.views.upload_image()
• addons.tasks.resize_preview()
• addons.tasks.resize_icon()

┆Issue is synchronized with this Jira Task