refactor(backend): reduce API surface by unifying metadata endpoints (#11035)

* replace individual metadata endpoints with a generic endpoint an a lot of permanent redirects

* remove more names

* reduce duplication more

* remove now unneeded tests

* update remaining tests to use urls

* bump api

* follow redirects in tests

* reduce new fncs

* fix redirect setup

* fix test

* update to fix schema collissions

* fix permission check

* simplify and fix lookup

* clone fork for now

* add changelog entry

* update api version date

* remove temporary change to python lib

* update docs

docs/docs/plugins/metadata.md

@@ -42,12 +42,7 @@ print(part.metadata)
 
 ### API Access
 
-For models which provide this metadata field, access is also provided via the API. Append `/metadata/` to the detail endpoint for a particular model instance to access.
-
-For example:
-
-{{ image("plugin/model_metadata_api.png", "Access model metadata via API", maxheight="400px") }}
-
+For models which provide this metadata field, access is also provided via the API. Use the generic `/metadata/<modelname>/<object id>/` endpoint to retrieve or update metadata information.
 
 #### PUT vs PATCH