Move resource synthesis for Service controller into resource subpackage.

[mattmoor]

This moves the assorted methods for constructing the resources owned by the Service controller into pkg/controller/service/resources.

I want a clearer separation of these trivial methods from the more complex controller logic because they should be trivial to unit test to nearly 100% and tracking that is harder when they are grouped with the harder-to-cover controller code.

I did this as a proof-of-concept, but think we should probably follow suit with the other controllers.

/assign @jonjohnsonjr

cc @tcnghia

[mattmoor]

FWIW, I also think that this is a significantly better place for the assorted naming methods to move, but that is not part of this change.

Something I didn't call out is that I simplified the names here to shorten them, with the expectation that if folks need to import multiple resources packages from different controllers (e.g. if we relocate naming methods) that they'd import:

import (
  svcresources "github.com/knative/serving/pkg/controller/service/resources"
  cfgresource "github.com/knative/serving/pkg/controller/configuration/resources"
)

... and that the package-qualification would become redundant with some of the qualification previously in the method name.

[knative-metrics-robot]

The following is the coverage report on pkg/. Say /test pull-knative-serving-go-coverage to run the coverage report again

File	Old Coverage	New Coverage	Delta
pkg/controller/service/resources/labels.go	Do not exist	100.0%
pkg/controller/service/resources/route.go	Do not exist	100.0%
pkg/controller/service/resources/configuration.go	Do not exist	100.0%

*TestCoverage feature is being tested, do not rely on any info here yet

[jonjohnsonjr]

/lgtm
/approve

[google-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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