external dependency definition file

## Summary

Please consolidate all external dependencies such as docker images (like alpine, busybox, postgres, zookeeper, kafka, clickhouse, nginx, exim) and package distributions (like buster debian) in one place so that this project can be easily installed and maintained behind highly firewalled and internet disconnect systems where package distribution systems like artifactory may be used.

## Motivation

More clearly define external dependencies to make maintaining necessary internal changes manageable.