Dynamic config reloading

[jjst]

Support loading fresh config files, instead of redeploying the whole app, for changesets/PRs that are pure config changes.

• Use https://www.dynaconf.com/
• Write a custom loader that checks against a git repo
• Change the github action workflow so that:
  ** It pushes the docker image to dockerhub
  ** It only buildsand pushes a docker image on changes to Dockerfile, src, requirements, and ignores changes to config, README