[SERV-1189] Add validator interface

[ksclarke]

• Further parameterize parts of the Docker image build
• Use exec in ENTRYPOINT for better process control
• Use sh in ENTRYPOINT to be able to use ENV properties
• Add HEALTHCHECK to Docker image
• Add first passes at Validator and CsvLocation
• Clean up obsolete ENVs that are now hard-coded in the Dockerfile
• Create unique job names for nightly and release to make ACT use easier
• Changed the way GA vars are handled to make ACT use easier
• Use tags to isolate functional tests (requiring Docker) from unit tests (standalone)
• Update project's README with the latest processes/documentation
• Remove Docker compose file, leaving manual steps, Makefile, or ACT as build options
• Switched to using fmt.Sprintf() instead of string concatenation in some of the tests