[functions][k8s] Store jobNamespace as part of function metadata

[sijie]

Motivation

Currently, we don't store jobNamespace as part of function metadata. If the broker restarts with a different job namespace, it will cause the function statefulset not deleted in the original job namespace and a new statefulset is created in the new job namespace.

In order to address the issue, we should consider adding the job namespace as part of function metadata when the function is created. Eventually, we should support updating the job namespace and handle the case the job namespace is changed at the function worker side.