feat: add new Opik Tracer (#6928)

* feat: add new Opik Tracer

This PR adds a new Tracer to sends traces and spans to Opik.

* Fix typo in docs

* Optimize Opik integration to reduce number of HTTP calls

* Add session_id and user_id to the Opik tracer

* Check Opik configuration on the client side before making a remote check

* Tackle documentation reviews

* Apply suggestions from code review

Co-authored-by: Jacques Verré <jverre@gmail.com>

* Fix one of the doc link

* Explicitely check for Opik environment variables before enabling the Opik tracer

* test: add opik tracing unit tests

---------

Co-authored-by: Nadir J <31660040+NadirJ@users.noreply.github.com>
Co-authored-by: Jacques Verré <jverre@gmail.com>
Co-authored-by: Ítalo Johnny <italojohnnydosanjos@gmail.com>

src/backend/tests/unit/services/tracing/test_tracing_service.py

@@ -135,6 +135,10 @@ def mock_tracers():
             "langflow.services.tracing.service._get_arize_phoenix_tracer",
             return_value=MockTracer,
         ),
+        patch(
+            "langflow.services.tracing.service._get_opik_tracer",
+            return_value=MockTracer,
+        ),
     ):
         yield
 
@@ -294,7 +298,7 @@ async def test_get_langchain_callbacks(tracing_service):
         assert tracer.get_langchain_callback_called
 
     # Verify returned callbacks list length
-    assert len(callbacks) == 4  # Four tracers
+    assert len(callbacks) == 5  # Five tracers
 
     # Cleanup
     await tracing_service.end_tracers({})