TOP-000: Update Makefile to facilitate testing remotely

This updates the Makefile to no longer use the KUBE_NAMESPACE variable to auto-construct a TANGO_HOST, and instead just requires us to specify the full TANGO_HOST ourselves.

Constructing it from the KUBE_NAMESPACE is a leftover from the ska-low-csp repo, where the TANGO_HOST had to match the environment it was deployed to. This is not the case here, so we don't need to know the k8s namespace when running tests.