Support kustomize

[michaelsauter]

Kustomize introduces a template-free way to customize application configuration that simplifies the use of off-the-shelf applications.

I believe support for kustomize would be a great addition to Tailor as an alternative to OpenShift Templates:

• kustomize is built-in to kubectl from Kubernetes 1.14 onwards, so it has great exposure in the community
• It has a different approach then OpenShift Templates, so it's not "the same thing just with different syntax"
• It fits well into the workflow of Tailor - instead of oc process one would just need to do kustomize build

For more information on kustomize, see it's introduction blog post.

[michaelsauter]

See https://github.com/opendevstack/tailor/commit/cb4f1a6c600a6652d7640b18879395b59aa2e0e6.