Add Django CMS 4 support

[stefanw]

Description

This PR makes djangocms-transfer roughly work with Django CMS 4.1 installations.
We needed import/export between different installations and this works for us.

Maybe this can be a starting point for a 4.1 compatible release.

Checklist

• I have opened this pull request against master
• I have added or modified the tests when changing logic
• I have followed the conventional commits guidelines to add meaningful information into the changelog
• I have read the contribution guidelines and I have joined #workgroup-pr-review on
  Slack to find a “pr review buddy” who is going to review my pull request.

Summary by Sourcery

Add support for Django CMS 4.1 in the djangocms-transfer package, enabling import/export functionality. Refactor methods to handle many-to-many relationships and related model fields more effectively, and simplify plugin import and export processes by removing unnecessary operations.

New Features:

• Add support for Django CMS 4.1 in the djangocms-transfer package, enabling import/export functionality between different installations.

Enhancements:

• Refactor the restore method to handle many-to-many relationships and related model fields more effectively.
• Simplify the import_plugins function by removing unnecessary tree order handling and plugin reordering.
• Improve the get_plugin_export_data function by removing the order_by clause for descendants.

[fsbraun]

@stefanw Thanks for this work. Looks good at first sight! I will review in more detail, but

• Uses API to create plugins 👍
• Respects CMS 4 toolbar object 👍 (here, we might need to look at separate code for v3 and v4)

[fsbraun]

@sourcery-ai review

[sourcery-ai]

Reviewer's Guide by Sourcery

This PR updates djangocms-transfer to be compatible with Django CMS 4.1 by refactoring the plugin import/export functionality and updating page content handling. The main changes focus on modernizing the plugin restoration process, handling many-to-many relationships, and adapting to Django CMS 4's new page content model.

Class diagram for updated plugin restoration process

classDiagram
    class PluginRestoration {
        +restore(placeholder, language, parent)
        -m2m_data: dict
        -data: dict
    }
    class CMSPlugin {
        +add_root()
        +set_base_attr()
    }
    class Model {
        +_meta: Meta
    }
    class Meta {
        +get_fields()
    }
    PluginRestoration --> CMSPlugin : uses
    PluginRestoration --> Model : uses
    Model --> Meta : has
    note for PluginRestoration "Handles plugin restoration with m2m relationships"

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Class diagram for updated page content handling

classDiagram
    class PageContent {
        +pk
        +get_slug(language)
    }
    class ExportImportForm {
        +cms_page: ModelChoiceField
        +get_filename()
    }
    ExportImportForm --> PageContent : uses
    note for ExportImportForm "Updated to use PageContent model"

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File-Level Changes

Change	Details	Files
Refactored plugin restoration logic to use modern Django CMS plugin API	Replaced manual plugin tree manipulation with add_plugin() function Added support for many-to-many relationships in plugin data Removed manual plugin reordering and tree order management Added handling for related model fields during plugin restoration	djangocms_transfer/datastructures.py
Updated toolbar integration for Django CMS 4 compatibility	Changed page draft handling to work with new page model Updated object type checking to use PageContent Modified edit mode detection logic	djangocms_transfer/cms_toolbars.py
Simplified plugin import and export process	Removed explicit plugin tree ordering Simplified descendant plugin handling Removed placeholder dirty marking	djangocms_transfer/importer.py djangocms_transfer/exporter.py
Updated form handling for new PageContent model	Changed queryset to use PageContent instead of Page model Updated slug retrieval to handle new page content structure	djangocms_transfer/forms.py

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[sourcery-ai]

Hey @stefanw - I've reviewed your changes - here's some feedback:

Overall Comments:

• Please add tests to verify the changes, especially around plugin restoration and page content handling. This will help ensure compatibility with Django CMS 4.1 without regressions.
• Follow the conventional commits guidelines to properly document these architectural changes in the commit history.

Here's what I looked at during the review

• 🟡 General issues: 1 issue found
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟡 Complexity: 1 issue found
• 🟢 Documentation: all looks good

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[sourcery-ai]

suggestion: Consider adding error handling for invalid many-to-many relations

The code silently ignores invalid PKs in many-to-many relations. Consider logging or raising warnings when related objects don't exist to prevent silent data loss.

                        requested_pks = m2m_data[field.name]
                        objs = field.related_model.objects.filter(pk__in=requested_pks)
                        if objs.count() != len(requested_pks):
                            logger.warning(
                                f"Some {field.name} relations could not be found: "
                                f"requested {len(requested_pks)}, found {objs.count()}"
                            )