* build(docker): refactor docker build scripts
- add "build" option to docker-compose files to simplify rebuilding of images
- create "start.sh" script so it's easier to override "command" in the quickstart's docker-compose file
- use dockerize to wait for requisite services to start up
- add a dedicated Dockerfile for kafka-setup
This fixes https://github.com/linkedin/datahub/issues/1549 & https://github.com/linkedin/datahub/issues/1550
As we're now utilize GitHub Actions to build & publish docker images to docker hub under linkedin org
Also allow overriding image tags via DATAHUB_VERSION environment variable
