Maureen wants an example Dockerfile to be provided via `igc enable` to use as a reference

**Summary**
igc enable should provide an example Dockerfile that works with our pipelines

**Is your feature request related to a problem? Please describe.**
This is an outcome from [issue # 178](https://github.com/ibm-garage-cloud/planning/issues/178)

The `igc enable` command works fine but, Buildah has issues building some Dockerfiles that don't follow some best practices.

**Describe the solution you'd like**
When we run the `igc enable` it should also create a Dockerfile example or template file that documents best practices to build the various types of projects.

**Describe alternatives you've considered**
When we run the `igc enable` we could replace the Dockerfile but I don't think that is a viable option because it would be impossible to configure one that would work for every project.

**Additional context**
This is a result of the work done on [issue # 178](https://github.com/ibm-garage-cloud/planning/issues/178)