Add integration tests to the project

[programmer04]

Kubernetes-telemetry is used in production by KIC, hence proper test suite should be added. Moreover creating unit tests with mocked client is tedious and may be error prone, because it requires some hack like e.g. in #143

envtest can be leveraged similarly as it's being done in KIC to spin up etcd and api-server, create those resources and assert that counters work.