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/make-admin-panel-api-request.util.ts

@@ -0,0 +1,24 @@
+import { ASTNode, print } from 'graphql';
+import request from 'supertest';
+
+/* global APP_PORT, ADMIN_ACCESS_TOKEN */
+
+type GraphqlOperation = {
+  query: ASTNode;
+  variables?: Record<string, unknown>;
+};
+
+export const makeAdminPanelAPIRequest = (
+  graphqlOperation: GraphqlOperation,
+) => {
+  const client = request(`http://localhost:${APP_PORT}`);
+
+  return client
+    .post('/graphql')
+    .set('Authorization', `Bearer ${ADMIN_ACCESS_TOKEN}`)
+    .send({
+      query: print(graphqlOperation.query),
+      variables: graphqlOperation.variables || {},
+    })
+    .expect(200);
+};