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

Start by locating the purge_instance_history_by entry point and the DTS backend request it makes, then reproduce the call with the runtime statuses and optional time bounds shown in the issue. Trace the 400 response and verify the operation succeeds and reports the expected number of deleted instances.

Written by the indexing model from the issue text.