NPD needs an integration test tier that contributors can run locally

[DigitalVeer]

We should add a test tier between unit tests and the GCE suite that can be run locally.

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NPD currently has two test tiers:

1. Unit tests
2. GCE e2e tests (Prow)

The e2e suite today only asserts against a local metrics endpoint on a GCE VM; yet, we cannot easily run the same functionality locally. This is because make e2e-test requires a GCP project, a zone, an image, and SSH keys. Not all important behaviors are unit-testable, and having the ability to run e2e tests locally will help author better improvements to NPD.

We should have two additional forms of testing to enable local e2e testing:

Form	What it covers	Sketch
Process-level	log parsing through condition/event	run NPD against fixed log files and assert emitted events against a local fake apiserver ( via --apiserver-override)
KIND	DaemonSet lifecycle, NodeCondition transitions	run NPD as a DaemonSet in a KIND cluster and inject faults, assert conditions and cleanup on shutdown

This pattern is the standard in other Kubernetes repositories. Kubernetes has an integration test tier and only merges PRs when unit, integration, and e2e tests all pass (https://github.com/kubernetes/community/blob/master/contributors/devel/sig-testing/testing.md). Furthermore, cert-manager and cilium run KIND-based e2e locally as well.

Together with #1328, this allows extensive coverage of NPD behavior before reaching a VM.

/sig node
/kind cleanup