👽 [#4057] Address breaking changes in zgw-consumers

Dropping gemma-zds-client means that we can't use any of its
API anymore.

src/openforms/contrib/kvk/migrations/0005_normalize_kvk_service_config.py

@@ -24,6 +24,10 @@ def set_kvk_service(apps, _):
     """
     Derive the "common" API root for KVK interaction.
 
+    NOTE: the explanation below is kept for historical reasons. The API specs are
+    separate and so are the services/config. We don't use the API specs anymore,
+    but API gateways caused issues. See migration 0007 which reverts this change.
+
     The zoeken/basisprofielen API's were historically separate services because they
     have their own OpenAPI specs and zgw_consumers requires api_root to be unique. Not
     doing this doesn't allow using zgw_consumers.Service.build_client (which needs the

src/openforms/prefill/management/commands/generate_prefill_from_spec.py

@@ -4,8 +4,9 @@
 from django.core.management import BaseCommand
 
 import black
+import requests
+import yaml
 from glom import GlomError, Path, glom
-from zds_client.oas import SchemaFetcher
 from zgw_consumers.models import Service
 
 from ...attributes_generator import OpenApi3AttributesGenerator
@@ -70,11 +71,18 @@ def select_schema(root_schema, api_schema):
         return None
 
 
+def fetch_schema(url: str) -> dict:
+    # fetch the schema and load as yaml. Note that JSON documents are also valid YAML.
+    response = requests.get(url)
+    response.raise_for_status()
+    root_schema = yaml.safe_load(response.content)
+    return root_schema
+
+
 def generate_prefill_from_spec_url(
     url, api_path="", api_schema="", use_embeds=False, command=""
 ):
-    schema_fetcher = SchemaFetcher()
-    root_schema = schema_fetcher.fetch(url)
+    root_schema = fetch_schema(url)
 
     # find the call with the http parameters we're interested in
     if not api_path and not api_schema:
@@ -333,7 +341,7 @@ def handle(self, **options):
 
         if url and not options["path"] and not options["schema"]:
             # be helpful and suggest paths and schemas
-            schema = SchemaFetcher().fetch(url)
+            schema = fetch_schema(url)
 
             if schema["paths"]:
                 self.stdout.write("path:")

src/openforms/submissions/tests/form_logic/test_fetching_form_variable_values_from_services.py

@@ -1,4 +1,3 @@
-from functools import lru_cache
 from pathlib import Path
 from typing import Any
 from unittest import skip
@@ -47,16 +46,6 @@ def setUpClass(cls):
             ),
         )
 
-        # prevent parsing the yaml over and over and over
-        cls.service.id = 1  # need pk for __hash__
-        # FIXME: update to new client approach
-        cls.service.build_client = lru_cache(1)(cls.service.build_client)
-
-        # populate the schema cache *before* any test runs, otherwise this causes flakiness
-        # in hypothesis tests
-        client = cls.service.build_client()
-        client.schema
-
     @requests_mock.Mocker()
     def test_it_performs_simple_get(self, m):
         m.get("https://httpbin.org/get", json={"url": "https://httpbin.org/get"})