Installing KnativeServing CR in namespace not named knative-serving doesn't configure the APIService correctly

[whitleykeith]

Describe the bug When installing the KnativeServing CR in namespace "foo", the operator also configures the APIService which always defaults to look for the knative-serving/autoscaler service. The autoscaler is not discoverable at that addresss

Expected behavior The APIService is configured to look for foo/autoscaler, assuming "foo" is the namespace the KnativeServing CR has been installed into.

To Reproduce Install a KnativeServing CR into a namespace not named "knative-serving"

Knative release version 0.11.0

[aliok]

IMO, this is more of a question if we would like to support installing Knative in any namespace. All the Knative documentation I can see instructs users to install things on specific namespaces.

We should do one of these:

Option A:

• We fix this problem
• We add some tests that install Knative into other namespaces and make sure things work fine
• We announce that we support this scenario

Option B:

• We don't fix this problem
• We add some validation to make sure the operator only accepts installation CRs from the specific namespace (similar to https://github.com/openshift-knative/serverless-operator/blob/master/knative-operator/pkg/webhook/knativeserving/webhook_validating.go#L140)
• We make sure operator installs Knative components into that same specific namespace
• We announce that we only support installing Knative in that specific namespace

cc @k4leung4 @houshengbo @jcrossley3

[aliok]

@markusthoemmes told me that Knative serving components should work fine in any namespace as they use system.Namespace(). So, let's fix this bug and make sure we have some tests for installing Knative into other namespaces.