Allow implicit namespace resolution in apply-time-mutation

[b1zzu]

I would like to create packages with config.kubernetes.io/apply-time-mutation that are independent of the namespace they are going to be deployed in.

Example:

Given this configuration:

apiVersion: v1
kind: ConfigMap
metadata:
  name: test-b
  annotations:
    config.kubernetes.io/apply-time-mutation: |
      - sourceRef:
          kind: ConfigMap
          name: test-a
        sourcePath: $.data.src
        targetPath: $.spec.dest
        token: ${value}
data:
  dest: "${value}-bar"
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: test-a
data:
  src: "foo"

when applying it to the cluster it fails with the following error:

error: invalid object: "default_test-b__ConfigMap": invalid "config.kubernetes.io/apply-time-mutation" annotation: external dependency: /namespaces/default/ConfigMap/test-b -> /ConfigMap/test-a

and force me to explicitly define the namespace of the source resources making the package impossible to reuse in different namespaces.