[fix] Added delete_confirmation_template attr in DeviceAdmin

[asmodehn]

Checklist

• I have read the OpenWISP Contributing Guidelines.
• I have manually tested the changes proposed in this pull request.
• I have written new test cases for new code and/or updated existing tests for changes to existing code.
• I have updated the documentation.

Description of Changes

This add delete_confirmation_template attr to the Device Admin class, just like other templates.
Without it, selenium deletion tests will fail on apps deriving from config, that are not named config.

[coderabbitai]

📝 Walkthrough

Walkthrough

A custom delete confirmation template is specified for the DeviceAdmin class by adding a delete_confirmation_template attribute that points to admin/config/device/delete_confirmation.html. This is a single-line configuration addition that does not alter any existing functionality or logic.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 1 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Title check	⚠️ Warning	The PR title uses the correct [type] format but uses [fix] when the change is actually an addition/feature. The summary indicates this adds a missing template attribute, which is a feature/change rather than a fix.	Update the title to use [change] or [feature] instead of [fix], such as '[change] Add delete_confirmation_template attr in DeviceAdmin' to accurately reflect that this adds a new attribute rather than fixing a bug.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description covers the core change and motivation, but lacks reference to an issue number and screenshots. Two checklist items remain unchecked.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[nemesifier]

@asmodehn if this is missing, you run into issues? Could you provide an example? Just double checking.

[asmodehn]

If I write a custom_config app with Admin classes that inherit from the config app, during the deletion (and without adding my own deletion template in the custom_config app), the template that django displays is the default "admin/delete_confirmation.html"
So in openwisp usecase, it means the "warning" part was skipped, so the deletion workflow ended up to be different

Note: this behavior is different than with other templates (as they are defined as attributes)

That behavior is explicited there :
https://github.com/django/django/blob/main/django/contrib/admin/options.py#L1769
Without that attribute, django assumes a default template name for this app, or replace it with its own default template.

[nemesifier]

Thanks for the explanation @asmodehn 🙏