feat: add parent plugin context

[metaforx]

In a current project, I extended DjangoCMS-Rest with a custom serializer for all custom CMS plugins to add the parent plugin type.

What does this solve?

• Switch layout/behavior in frontend for the plugin depending on the context.

[fsbraun]

That's common place when rendering plugins traditionally in templates.

[metaforx]

That's common place when rendering plugins traditionally in templates.

So you agree that this is very helpful and a needed add-on. AFAIK djangocms-rest does not provide this yet.
Likely we can use the same pattern to gather this info as the CMS does when rendering plugins in templates.

[metaforx]

@fsbraun This works well enough to extend custom plugins, but it might not be the best possible implementation.

class CMSParentPluginSerializer(serializers.ModelSerializer):
    """Return the parent plugin type if it exists"""

    parent_plugin_type = serializers.SerializerMethodField()

    def get_parent_plugin_type(self, obj) -> str:
        parent = obj.parent
        return parent.plugin_type if parent else None