Starter Kit: CI/CD with Github Actions

### Background on the problem the feature will solve/improved user experience
Manual cloud deployments are tedious.

### Describe the solution you'd like
Once we've validated our manual deployments we would like to have CI/CD to deploy easily to cloud across all Open Sentencing repositories.

### Tasks

Add github actions for:
- [ ] building
- [ ] unit testing
- [ ] accessibility testing
- [ ] linting
- [ ] deployment

Related Issues:
- https://github.com/Call-for-Code-for-Racial-Justice/Open-Sentencing-Aggregator/issues/30
- https://github.com/Call-for-Code-for-Racial-Justice/Open-Sentencing-Aggregator/pull/20
- https://github.com/Call-for-Code-for-Racial-Justice/Open-Sentencing/issues/28
- https://github.com/Call-for-Code-for-Racial-Justice/Open-Sentencing-Aggregator/issues/28
- https://github.com/Call-for-Code-for-Racial-Justice/Open-Sentencing-UI/issues/63

### Acceptance Criteria

Beginne damit, die verwandten Issues und den Pull Request zu prüfen, insbesondere Aggregator issue 30 und PR 20, um den bestehenden manuellen Deployment-Prozess über mehrere Repositories hinweg zu verstehen. Das Issue nennt keine Dateien, Tests, keinen Cloud-Anbieter und keine Akzeptanzkriterien; für den Abschluss müssten Workflows für das Bauen, Unit-Tests, Accessibility-Tests, Linting und Deployment abgedeckt werden.

Vom Indexierungsmodell aus dem Issue-Text verfasst.