Add `@types/jest` npm package as a dev dependency

What does this MR do and why?

In vscode, and I assume in other IDEs, adding @types/jest to the package.json enables both intellisense and documentation for jest test files (*_spec.js).

See this comment about why @types/jest and not @jest/types

This commit is the result of running this command: yarn add -D '@types/jest@^26.0.24'

Screenshots or screen recordings

See code completion in action in vscode when this package is added:

Screen_Recording_2022-03-17_at_15.07.17

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.