Fixing some API generation stuff, bit of cleanup (#162)

Figured out where the BasePermissionMetaclass error was coming from - "auth" in extend_schema isn't for what I was using it for. Also resolved some issues where ID types weren't being figured out, and where depth was tripping up the generator. Regenerated the OpenAPI spec.

Also cleaned up a few things while in here:
- Removed BasketItemViewSet (not used - we'll want a delete-only one later but for now it's not particularly useful)
- Updated BasketWithProductSerializer to pull some discount fields that aren't here (yet)
- Updated basket serializers in general - this had methods to pull stuff where we could just pass the serializer
- Updated basket endpoints that return stuff to use the ones with product info by default
- Updated BasketViewSet to just be a regular ReadOnlyModelViewSet and limit it to the current user's baskets

frontends/api/src/generated/v0/.openapi-generator-ignore

@@ -21,3 +21,8 @@
 #docs/*.md
 # Then explicitly reverse the ignore rule for a single file:
 #!docs/README.md
+
+**/.npmignore
+**/.gitignore
+**/git_push.sh
+**/.openapi-generator-ignore