Add Kubernetes deployment resources and document

[onelittlenightmusic]

This PR enables users to deploy webspoon on Kubernetes easily.

Committed changes

• Created Kubernetes resource files (deployment.yaml & service.yaml)
• Added k8s directory to collect Kubernetes
• Added k8s/README.md to describe how to deploy these resources to Kubernetes

ToDos

• ConfigMap to customize web.xml
• Create helm chart
  • Clarify customization points and embed into values.yaml

[onelittlenightmusic]

Thank you for comments. Could you please check the changes?