update replicas will cause all pods been rescheduled
when updating replicas for a sink, all pods will be rescheduled, which is not expected behaviour. Should fix this BUG and add related tests.
This is because the FunctionDetails have been passing as STS container template command and the FunctionDetails is changing when replicas changed.
seems the parallelism is getting from the spec.replicas, since we are using k8s for auto-scaling, how about setting the parallelism to hardcoded 1?
I have a proposal to use a proxy service to provide the ability for pulsar functions managed by Function Mesh to interact with the cluster.

In a preliminary idea, this service should provide the following interfaces.
- Get the replicas number of the function
- Get the status of the function