Twenty config integration tests + conversion refactor (#11972)

- In this PR the default value of IS_CONFIG_VARIABLES_IN_DB_ENABLED has
been changed to true,
    
- This is my first time writing integration tests, so I’d appreciate a
thorough review. :)
I’ve tried to follow the existing test patterns closely, but there might
be some small mistakes I may have missed.
Also let me know if I have missed any important test cases that should
be tested

UPDATE - 
### Config Value Converter Refactoring
- Created a centralized type transformers registry with bidirectional
validation
- Refactored ConfigValueConverterService to support validation in both
directions:
- Maintained existing DB-to-app conversion behavior
- Added validation for app-to-DB conversion
- Added integration tests to verify validation works in both directions

---------

Co-authored-by: Félix Malfait <felix@twenty.com>

packages/twenty-server/test/integration/twenty-config/utils/delete-config-variable.util.ts

@@ -0,0 +1,28 @@
+import { PerformTwentyConfigQueryParams } from 'test/integration/twenty-config/types/perform-twenty-config-query.type';
+
+import {
+  DeleteConfigVariableFactoryInput,
+  deleteConfigVariableQueryFactory,
+} from './delete-config-variable.query-factory.util';
+import { makeAdminPanelAPIRequest } from './make-admin-panel-api-request.util';
+
+export const deleteConfigVariable = async ({
+  input,
+  expectToFail = false,
+}: PerformTwentyConfigQueryParams<DeleteConfigVariableFactoryInput>) => {
+  const graphqlOperation = deleteConfigVariableQueryFactory({
+    key: input.key,
+  });
+
+  const response = await makeAdminPanelAPIRequest(graphqlOperation);
+
+  if (!expectToFail) {
+    expect(response.body.data).toBeDefined();
+    expect(response.body.errors).toBeUndefined();
+    expect(response.body.data.deleteDatabaseConfigVariable).toBeDefined();
+  } else {
+    expect(response.body.errors).toBeDefined();
+  }
+
+  return { data: response.body.data, errors: response.body.errors };
+};