Remove the Docker base images

[adrianclay]

Why

There appears to be a 1-2-1 mapping between actual image, and base image.

This layer of indirection doesn't appear to be adding any value to the MHS Adaptor, and in fact makes it harder to release as there are two separate images for each of the inbound,outbound,sds.

By combining the base image into the actual image this will simplify maintenance for the developers.

Type of change

Internal change (non-breaking change with no effect on the functionality affecting end users)

Checklist:

• I have performed a self-review of my code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have updated the Changelog with details of my change in the UNRELEASED section if this change will affect end users