Enable Tekton Chains to operate only in selected namespaces

Currently Tekton Chains controller support the below flag to restrict chains operate in a single namespace. because knative injection.WithNamespaceScope does not support multi namespaces

• https://github.com/tektoncd/pipeline/blob/main/cmd/controller/main.go#L47
• https://github.com/tektoncd/chains/blob/main/cmd/controller/main.go#L44
  However, the users want a choice to operate in couple of namespace instead of just one.