Unit tests and CI

[rahulbot]

Here is a very basic first pass at running simple unit tests (#36). This leverages GitHub workflows and the Elasticsearch Docker release to create a dummy index that looks like our real one. Then it spins up the API server and queries a few basic elements. This isn't exhaustive, but works locally.

Some notes:

• The mappings are copied from story-indexer for now and replicated in test.create_fixtures.py. Is there a clever way to automatically keep that in sync?
• I had to move the requirements out of the Dockerfile and into requirements.txt. I don't think this messed up the docker build but I'm not an expert there.
• I removed some workflows that looked un-related to our fork of this repo.
• I hard-coded to python 3.10 and elasticsearch 8.8.2. My poking around suggested that matched what we're using in other places.

[rahulbot]

Yes - the CI can build a versioned and tagged image and push to Docker. I had previously put some notes on that approach in #5.

[rahulbot]

(merged because I need these fixes for web-UI search integration testing)