[15.0][ADD] attachment_mimetype_restriction

[AungKoKoLin1997]

This module blocks specific MIME types from being uploaded as attachments using content-based detection rather than filename extensions. This prevents uploading potentially dangerous files (executables, scripts, etc.).

@qrtl QT5832

[NL66278]

👍 LGTM

[SanamiK]

Here is a summary of what I tested and the issues I found.

What I tested
I tried to attach a non-allowed type file in Send Invoice dialog in the Invoicing module.

Issue 1: Internal Odoo files are incorrectly blocked
Before even attaching a file, internal Odoo operations were being blocked. Configuring the document layout (company logo, font, or colors) triggers a ValidationError for text/scss.

Issue 2: Adding text/scss to the allowlist causes a different error
As a workaround for Issue 1, I added text/scss to the allowlist. This time, an application/octet-stream error occurred. It appears that legitimate files(PDF) processed internally by Odoo are also being blocked.

Issue 3: Users are not shown a meaningful error message in some cases
When a user tries to attach a non-allowed file type, the generic message "Something horrible happened" is shown instead of a specific validation message. The user has no way to tell what went wrong.

[SanamiK]

Functional review. LGTM!

I checked the behavior with settings applied to all models and settings applied to individual models.

[OCA-git-bot]

This PR has the approved label and has been created more than 5 days ago. It should therefore be ready to merge by a maintainer (or a PSC member if the concerned addon has no declared maintainer). 🤖