✨(backend) use langfuse to monitor AI actions

We want to monitor AI actions. For this we choose to use langfuse. As
this usage is optional, we load langfuse sdk only if settings are
configured. Also, the openai client from langfuse is a dropin
replacement of openai client, so we only have to change how openai is
imported.

src/backend/core/services/ai_services.py

@@ -3,10 +3,14 @@
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 
-from openai import OpenAI
-
 from core import enums
 
+if settings.LANGFUSE_PUBLIC_KEY:
+    from langfuse.openai import OpenAI
+else:
+    from openai import OpenAI
+
+
 AI_ACTIONS = {
     "prompt": (
         "Answer the prompt using markdown formatting for structure and emphasis. "