While in no way complete - this is a first pass at a server that can
do what we want:
* Accept messages from multiple kafka topics and pass them to a command as
  standard input
* Check the command's exit status and log it
* Stop consuming jobs when a release information file signals there is a 
  newer version of the software available
* Exit with status code 0 when successfully stopped, and with 1 in case of 
  a fatal error, allowing the orchestrator to restart the server if needed

There are quite a bit of things still missing, including metrics reporting,
better logging, and more tests scenarios (including an integration test
environment using either devcontainer or docker-compose).

Bug: T355292