Update with-jest packages and docs

[delbaoliveira]

This PR updates the with-jest example to the latest version of Jest and adds a note about the Jest and RTL testing environments (related to this discussion). Also adds minor tweaks to the testing docs.

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• Integration tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.
• Errors have helpful link attached, see contributing.md

Documentation / Examples

• Make sure the linting passes