DTS - purge_instance_history_by throws "Exception: The operation failed with an unexpected status code 400"

🐛 **Describe the bug**
If you call purge_instance_history_by when using the DTS backend, you get the following error: Exception: The operation failed with an unexpected status code 400

🤔 **Expected behavior**
purge_instance_history_by should successfully purge instance history based on the input params

☕ **Steps to reproduce**
Function code:

```python
@bp.route(route="PurgeOrchestrationHistory", methods=["GET", "POST"])
@bp.durable_client_input(client_name="client")
async def purge_history(req: func.HttpRequest, client: df.DurableOrchestrationClient):
logging.info("Starting purge all instance history")
try:
# Parse optional query parameters for purgeStartTime and purgeEndTime
purge_start_time: Optional[datetime] = None
purge_end_time: Optional[datetime] = None
if req.params.get("purgeStartTime"):
purge_start_time = datetime.fromisoformat(req.params["purgeStartTime"])
if req.params.get("purgeEndTime"):
purge_end_time = datetime.fromisoformat(req.params["purgeEndTime"])

# Purge orchestration history
result = await client.purge_instance_history_by(
created_time_from=purge_start_time,
created_time_to=purge_end_time,
runtime_status=[
df.OrchestrationRuntimeStatus.Completed,
df.OrchestrationRuntimeStatus.Failed,
df.OrchestrationRuntimeStatus.Terminated,
],
)
logging.info("Finished purge all instance history")
return func.HttpResponse(
f"Purged {result.instances_deleted} records",
status_code=200,
mimetype="text/plain"
)
except Exception as ex:
logging.error("Failed to purge all instance history", exc_info=True)
return func.HttpResponse(
f"Failed to purge all instance history: {str(ex)}",
status_code=500,
mimetype="text/plain"
)
```

⚡**If deployed to Azure**
N/A

首先定位 purge_instance_history_by 入口点及其发出的 DTS 后端请求，然后使用 issue 中所示的运行时状态和可选时间范围重现该调用。跟踪 400 响应，并验证操作成功且报告了预期的已删除实例数量。

由索引模型根据 Issue 内容生成。