[Walking Skeleton] Implement/Package plugin che-hello-world

[l0rd]

• Implement the Che plugin necessary for User Story 2 in ws.next walking skeleton #10123
  • hello-world service that runs in a sidecar container (with image published on docker hub)
  • theia front end plugin
• Create the meta.yaml, che-plugin.yaml, dependencies.yaml
• Package che-plugin.yaml, dependencies.yaml and theia plugin in a tar.gz and publish it as a github repository release page

For the format of the files refer to the architectural details section in #10123

[benoitf]

available at https://github.com/ws-skeleton