chore: deprecate allow_turn_resume (#1377)

# What does this PR do?

- Deprecate allow_turn_resume flag as this is used for staying backward
compat.
- Closes https://github.com/meta-llama/llama-stack/issues/1363

[//]: # (If resolving an issue, uncomment and update the line below)
[//]: # (Closes #[issue-number])

## Test Plan
```
LLAMA_STACK_CONFIG=fireworks pytest -v tests/api/agents/test_agents.py --inference-model "meta-llama/Llama-3.3-70B-Instruct" --record-responses
```

<img width="1054" alt="image"
src="https://github.com/user-attachments/assets/d31de2d4-0953-41e1-a71a-7e1579fa351a"
/>


[//]: # (## Documentation)

docs/_static/llama-stack-spec.html

@@ -5303,9 +5303,6 @@
                     },
                     "tool_config": {
                         "$ref": "#/components/schemas/ToolConfig"
-                    },
-                    "allow_turn_resume": {
-                        "type": "boolean"
                     }
                 },
                 "additionalProperties": false,