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)

llama_stack/apis/agents/agents.py

@@ -296,9 +296,6 @@ class AgentTurnCreateRequest(AgentConfigOverridablePerTurn):
     stream: Optional[bool] = False
     tool_config: Optional[ToolConfig] = None
 
-    # TODO (xiyan): temporary flag, will remove for 0.1.5
-    allow_turn_resume: Optional[bool] = False
-
 
 @json_schema_type
 class AgentTurnResumeRequest(BaseModel):
@@ -355,7 +352,6 @@ class Agents(Protocol):
         documents: Optional[List[Document]] = None,
         toolgroups: Optional[List[AgentToolGroup]] = None,
         tool_config: Optional[ToolConfig] = None,
-        allow_turn_resume: Optional[bool] = False,
     ) -> Union[Turn, AsyncIterator[AgentTurnResponseStreamChunk]]: ...
 
     @webmethod(