Add final_answer prompt template in correct format

prompts.yaml

@@ -181,6 +181,11 @@
 
   Now Begin! If you solve the task correctly, you will receive a reward of $1,000,000.
 
+"final_answer": |-
+  You have reached the final step of your task. Use the final_answer tool to submit your answer.
+  The answer should be clear, concise, and directly address the original question.
+  Format: final_answer(your_answer)
+
 "planning":
   "initial_facts": |-
     Below I will present you a task.