Add kcp backend example

[mjudeikis]

This adds a basic kube-bind kcp backend example.

This is not the final state of this. It is still missing documentation of how to get something running (same mangodb for now, but we need a better example).
Added a small Roadmap section too to specify what is planned next.

For now, it shares a lot of code with backend-example but I think its ok, as they will diverge in time. And later on we can see how we can externalize some of these into some library to be shared.

ps. This is monster PR, Any ideas on how to make it smaller?

TODO in follow-ups:

1. Add e2e tests
2. Add build for binaries and images on releases
3. Update readme with usage example
4. Start burning down roadmap in the readme.

[mjudeikis]

superceded by #275