refactor(api): enhance request handling and time management

- Initialized `response` variable in `trigger.py` to ensure proper handling in the trigger endpoint.
- Updated `http_parser.py` to conditionally set `CONTENT_TYPE` and `CONTENT_LENGTH` headers for improved robustness.
- Changed `datetime.utcnow()` to `datetime.now(UTC)` in `sqlalchemy_workflow_trigger_log_repository.py` and `rate_limiter.py` for consistent time zone handling.
- Refactored `async_workflow_service.py` to use the public method `get_tenant_owner_timezone` for better encapsulation.
- Simplified subscription retrieval logic in `plugin_parameter_service.py` for clarity.

These changes improve code reliability and maintainability while ensuring accurate time management and request processing.

api/controllers/trigger/trigger.py

@@ -26,6 +26,7 @@ def trigger_endpoint(endpoint_id: str):
         TriggerService.process_endpoint,
         TriggerSubscriptionBuilderService.process_builder_validation_endpoint,
     ]
+    response = None
     try:
         for handler in handling_chain:
             response = handler(endpoint_id, request)