Write Dockerfile for OBP-API

Is your feature request related to a problem? Please describe.

There is presently no in-repo Dockerfile (aka Containerfile) for OBP-API.

Describe the solution you'd like
As a developer I can build & run a container for OBP-API from within this repo.

Describe alternatives you've considered
It is best practice to keep container files within the same repo as their code where reasonable.

With this completed, the OBP-Docker repo should/must be deleted as redundant.

Additional context

See:

• https://github.com/tawoe/OBP-API/blob/2d7ef5c04e05aff09045c1cefb00d1ac99b40e50/Dockerfile#L1
• https://github.com/chrisjsimpson/obp-kubernetes/blob/master/Dockerfile (much older)

Be aware that layer caching is now a thing, the current attempts of the container file take a long time to re-build since there's no caching- this may be addressed with layer caching at build time.

Start by comparing the referenced Dockerfiles in the OBP-API and OBP-Kubernetes repositories, then inspect this repository's Scala build and runtime entry points. Create a root Dockerfile that builds and runs OBP-API with effective layer caching. Done means the image can be built and the API run from this repository, making the separate OBP-Docker repository redundant.