scheduledworkflow rock: Substitution of environment variable `NAMESPACE` is incorect

As seen in issue canonical/kfp-operators#352, specifically the comment: canonical/kfp-operators#352 (comment)
In the scheduledworkflow rock used in kfp-schedwf charm, the substitution of the environment variable NAMESPACE never happens. The command is:

pipelines-rocks/scheduledworkflow/rockcraft.yaml

Line 13 in 29df90c

command: /bin/controller --logtostderr=true --namespace=${NAMESPACE}

we can see that the substitution doesn't happen from the logs:

2023-10-13T09:29:08.022Z [controller] E1013 09:29:08.022113      15 reflector.go:138] pkg/mod/k8s.io/client-go@v0.23.3/tools/cache/reflector.go:167: Failed to watch *v1alpha1.Workflow: failed to list *v1alpha1.Workflow: workflows.argoproj.io is forbidden: User "system:serviceaccount:kubeflow:kfp-schedwf" cannot list resource "workflows" in API group "argoproj.io" in the namespace "${NAMESPACE}"

the namespace was passed as ${NAMESPACE}, this needs to be fixed in the rock.

and the namespace is hardcoded to kubeflow:

pipelines-rocks/scheduledworkflow/rockcraft.yaml

Line 16 in 29df90c

NAMESPACE: "kubeflow"

this is an issue because then scheduled workflows in other namespaces will not run.
we should align with the configuration in upstream.