Add tests for encoding collections in JSON for KEP-5116

Used test cases from:
* Original PR kubernetes#129334
* KEP https://github.com/kubernetes/enhancements/tree/master/keps/sig-api-machinery/5116-streaming-response-encoding#unit-tests

For now testing current serializer implementation to show encoder
behavior and agree on set of tests. Having a separate PR should make review easier.
In separate PR will add the implementation for streaming that should
provide same response byte-to-byte.

Author: serathius