docs: added docstrings to bdi_core and BeliefSetter behaviour

ref: N25B-197

src/control_backend/agents/bdi/behaviours/belief_setter.py

@@ -10,10 +10,13 @@ from control_backend.core.config import settings
 
 class BeliefSetter(CyclicBehaviour):
     """
-    TODO: docs
+    This is the behaviour that the BDI agent runs.
+    This behaviour waits for incoming message and processes it based on sender.
+    Currently, t only waits for messages containing beliefs from Belief Collector and adds these to its KB.
     """
     agent: BDIAgent
     logger = logging.getLogger("BDI/Belief Setter")
+    
     async def run(self):
         msg = await self.receive(timeout=0.1)
         if msg: