eventonica-react: get the cohort started testing APIs with Jest in general, then add directions for testing their project backend

[alodahl]

eventonica-react: get the cohort started testing APIs with Jest in general, then add directions for testing their project backend

1. Add a file in https://github.com/Techtonica/curriculum/blob/main/testing-and-tdd, ideally in the context of a create-react-app, that introduces testing APIs with Jest.

   • Note that this would come after https://github.com/Techtonica/curriculum/blob/main/testing-and-tdd/jest.md, so they have already had an intro to Jest.

2. Make changes so that this file’s directions make it easy to add Jest API testing to their eventonica-react project: https://github.com/Techtonica/curriculum/blob/main/project-example/week-9/eventonica/eventonica-test-api.md I would give them a few actual examples of tests they need in their eventonica-react project, and then try to be explicit about what else they should cover on their own.

See #1608 for more context.