Merge develop onto main for 0.3.0 release

[amoeba]

This probably doesn't need a code review but I'd recommend testing it out by installing to the dev cluster and reviewing the results from there.

Changes:

• Upgraded from Python 2 to 3
• Complete rewrite using a much cleaner codebase and new patterns
• Restructured code to follow recommended Python packaging guidelines
• Added a first pass of a CLI for interacting with the service (not done yet)
• Refactored tests into unit and integration sub-suites. pytest defaults to running just unit and pytest --integration runs all tests.
• Primary deployment strategy switched from Docker Compose to Kuerbernetes (via Helm). Docker Compose still supported.
• Rewrote triplification pattern to match Schema.org/Science-on-Schema pattern
• Added Sphinx documentation
• GitHub Actions Workflows for
  • Unit tests (pytest)
  • Sphinx documentation build and push to GitHub Actions
• Container images use ghcr.io instead of Docker Hub

Remaining TODOs before merge:

• [x] Remove old deploy YAML files
• [x] Confirm the persistent volume configuration

TODO after merge:

• [ ] Turn on GitHub Pages on this repo to enable the sphinx docs build
• [ ] Tag and create a 0.3.0 Release
• [ ] Decomission slinkythegraph DockerHub account (@ThomasThelen )