Suggest using userEvent library instead of fireEvent for simulating user interaction

[petermakowski]

userEvent adds related event calls from browsers to make tests more realistic than its counterpart fireEvent, which is a low-level api.

This makes for a more user-centric, and closer-to-truth testing of user interactions.

• add eslint rule https://github.com/testing-library/eslint-plugin-testing-library/blob/main/docs/rules/prefer-user-event.md

[bartaz]

Triaging as consideration for new architecture.