Epic: Refactor Test Suite

[drewbo]

As part of a broader React and related dependency upgrade, we likely need to significantly change our current test suite:

• the primary test renderer enzyme does not have a supported adapter for React 18
• the current React recommendation for test frameworks is to use jest and react-testing-library; these seemingly have better integration with newer React features than enzyme or mocha

Notes

• React Testing Overview
• React Testing Environments
• Jest
• React Testing Library
• RTL: migrate from enzyme

### Tasks
- [ ] https://github.com/cloud-gov/pages-core/pull/4613
- [ ] https://github.com/cloud-gov/pages-core/issues/4616
- [ ] https://github.com/cloud-gov/pages-core/issues/4617
- [ ] https://github.com/cloud-gov/pages-core/issues/4631
- [ ] https://github.com/cloud-gov/pages-core/issues/4635
- [ ] https://github.com/cloud-gov/pages-core/issues/4643
- [ ] https://github.com/cloud-gov/pages-core/issues/4642
- [ ] https://github.com/cloud-gov/pages-core/issues/4670
- [ ] https://github.com/cloud-gov/pages-core/issues/4669
- [ ] https://github.com/cloud-gov/pages-core/issues/4672
- [ ] https://github.com/cloud-gov/pages-core/issues/4668
- [ ] https://github.com/cloud-gov/pages-core/issues/4671
- [ ] https://github.com/cloud-gov/pages-core/issues/4665
- [ ] Decide how to generate and store fixtures
- [ ] Retire old tests
- [ ] Outline tests to be added