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>

doc/api/resources/events.rst

@@ -424,9 +424,9 @@ Endpoints
    :param organizer: The ``slug`` field of the organizer of the event to create.
    :param event: The ``slug`` field of the event to copy settings and items from.
    :statuscode 201: no error
-   :statuscode 400: The event could not be created due to invalid submitted data.
+   :statuscode 400: The event could not be updated due to invalid submitted data.
    :statuscode 401: Authentication failure
-   :statuscode 403: The requested organizer does not exist **or** you have no permission to create this resource.
+   :statuscode 403: The requested organizer does not exist **or** you have no permission to update this resource.
 
 
 .. http:patch:: /api/v1/organizers/(organizer)/events/(event)/