Investigate splitting Jest configuration per workspace

[romaricpascal]

What

Find out which benefits we get from splitting our Jest configuration per workspace (for ex. improving the behaviour of npx jest --watch which watches the whole repository or avoiding Jest being too eager to re-run tests on file changes).

Why

Ported from #4169 but we've mentioned it previously

For example, to avoid overlap we could replace complex Jest project wildcards with workspace jest.config.mjs files that can be configured and run separately:

export default {
  projects: [
    '<rootDir>/packages/*',
    '<rootDir>/shared/*',

    // Tasks
    '<rootDir>/packages/*/tasks/*',
    '<rootDir>/packages/*/tasks/*',
  ]
}

Who needs to work on this

Developers

Who needs to review this

Developers

Done when

• More details have been added to the issue
• Investigation has happened and changes made based on its results