docs: Add guardrail attribute documentation and examples (#3139)

- Document string-based guardrails in tasks
- Add guardrail examples to YAML configuration
- Fix Python code formatting in PT-BR CLI docs

docs/pt-BR/concepts/cli.mdx

@@ -76,6 +76,7 @@ Exemplo:
 crewai train -n 10 -f my_training_data.pkl
 ```
 
+```python
 # Exemplo de uso programático do comando train
 n_iterations = 2
 inputs = {"topic": "Treinamento CrewAI"}
@@ -89,6 +90,7 @@ try:
     )
 except Exception as e:
     raise Exception(f"Ocorreu um erro ao treinar a crew: {e}")
+```
 
 ### 4. Replay