**What this PR does / why we need it**:
This is to allow disable `enableServiceLinks` so that the service
environments are not injected into the pods where in my scenario Loki is
deployed in the same namespace as the Knative services resulted the Loki
pod unable to start up due to too many service environment being
injected.
Reference issue for pod unable to startup due to too many services:
https://github.com/kubernetes/kubernetes/issues/84539#issue-514261281
Co-authored-by: Trevor Whitney <trevorjwhitney@gmail.com>