Add Python integration tests

[dacharyc]

This PR builds on #27 and adds the following:

• Renames the existing test_movie_routes.py file to tests_movie_schemas.py, since those tests are really just testing the Pydantic models
• Adds a new test_movie_routes.py file with mocks to unit test the mocks. These tests identified a bug we need to resolve, and we'll need to update the tests after we do.
• Adds a new integration test directory with integration tests against a running FastAPI server instance
• Adds a README with info about the tests
• Updates the GitHub workflow to run the unit tests and integration tests as separate steps, and report on them discretely in the summary

[shuangela]

lgtm % one nit.