cmd/k8s-operator: add e2e tests for Connector resources (#20650)

This commit adds 3 end-to-end tests to the suite for the
operator's `Connector` resources. Connectors are used
to deploy subnet routers, exit nodes & app connectors
within a Kubernetes cluster.

One test exists for each respective mode of the resource
and assertions are made against control that the machine
is running in the expected mode using the device identifier
within the pod's state secret.

Closes: https://github.com/tailscale/corp/issues/38025

Signed-off-by: David Bond <davidsbond93@gmail.com>