Integrate che-plugin-registry deployment with the deployments of Che on k8s

[garagatyi]

Description

Would be useful to integrate che-plugin-registry deployment with Che deployments on OS/k8s to ease usage of Walking skeleton flow.
At least, we can add documentation on when to get deployment description (che-plugin-registry repo) and what should we do in Che deployment to use it.
We will also need deployment files for k8s (for example via helm) since now che-plugin-registry has only OS-specific deployment.

Reproduction Steps

OS and version:

Diagnostics:

[garagatyi]

@skabashnyuk hasn't it have been addressed already?

[garagatyi]

Outdated