Dockerized it and made it Kubernetes-friendly

[vgribok]

Change Summary

• Bug fix: command line option usage information was not printed when no cmd line args are supplied.
• Bug fix: Target Endpoint URL contains garbage ("undefined" suffix), if OAS has URL with no base path.
• New feature: ability to override target URL by via command line argument.
• New feature: added Dockerfile and corresponding section in the docs, to enable running the tool in the Docker container.
• New feature: added a reference/sample Helm chart, and corresponding MD docs, as a blueprint for those wishing to integrate Apigee proxy generation into their Kubernetes-based CI/CD pipeline.