Organizer-level plugins (#5305)

* Add version notes to the docs

* Adapt signal handling

* Add UI

* Add API

* API and tests

* Fix registry

* Update doc/development/api/plugins.rst

Co-authored-by: Felix Rindt <felix@rindt.me>

* Fix failing tests

* Apply suggestions from code review

Co-authored-by: Richard Schreiber <schreiber@rami.io>

* Update src/pretix/control/templates/pretixcontrol/organizers/plugin_events.html

Co-authored-by: luelista <weller@rami.io>

* Update src/pretix/control/templates/pretixcontrol/organizers/plugins.html

Co-authored-by: luelista <weller@rami.io>

* Update src/pretix/control/templates/pretixcontrol/organizers/plugins.html

Co-authored-by: luelista <weller@rami.io>

* Update src/pretix/control/navigation.py

Co-authored-by: luelista <weller@rami.io>

* Update src/pretix/control/urls.py

Co-authored-by: luelista <weller@rami.io>

* Apply suggestion from @wiffbi

* REbase migration

* Fix review note

* Fix test cases

* Remove plugin from all events if disabled on org level

* Update doc/development/api/plugins.rst

* Unify registries

* Rebase migration

---------

Co-authored-by: Felix Rindt <felix@rindt.me>
Co-authored-by: Richard Schreiber <schreiber@rami.io>
Co-authored-by: luelista <weller@rami.io>

src/pretix/api/serializers/fields.py

@@ -109,3 +109,19 @@ class UploadedFileField(serializers.Field):
             return None
         request = self.context['request']
         return request.build_absolute_uri(url)
+
+
+class PluginsField(serializers.Field):
+
+    def to_representation(self, obj):
+        from pretix.base.plugins import get_all_plugins
+
+        return sorted([
+            p.module for p in get_all_plugins()
+            if not p.name.startswith('.') and getattr(p, 'visible', True) and p.module in obj.get_plugins()
+        ])
+
+    def to_internal_value(self, data):
+        return {
+            'plugins': data
+        }