Adds mockCurrentUser() to API-side Jest

[cannikin]

Thanks @peterp!

This is beautiful because the syntax matches mockCurrentUser() on the web-side:

// service
export const deleteComment = ({ id }) => {
  requireAuth({ role: 'moderator' })
  return db.comment.delete({
    where: { id },
  })
}

// test
scenario('deletes a comment', async (scenario) => {
  mockCurrentUser({ roles: ['moderator'] })

  const comment = await deleteComment({
    id: scenario.comment.jane.id,
  })
  expect(comment.id).toEqual(scenario.comment.jane.id)

  expect(
    await db.comment.findUnique({ where: { id: scenario.comment.jane.id } })
  ).toEqual(null)
})

Closes #680

[github-actions]

📦 Packages for this PR can be downloaded from
https://rw-pr-redwoodjs-com.s3.amazonaws.com/1624/create-redwood-app-0.22.1-20d4d96.tgz
https://rw-pr-redwoodjs-com.s3.amazonaws.com/1624/redwoodjs-api-0.22.1-20d4d96.tgz
https://rw-pr-redwoodjs-com.s3.amazonaws.com/1624/redwoodjs-api-server-0.22.1-20d4d96.tgz
https://rw-pr-redwoodjs-com.s3.amazonaws.com/1624/redwoodjs-auth-0.22.1-20d4d96.tgz
https://rw-pr-redwoodjs-com.s3.amazonaws.com/1624/redwoodjs-cli-0.22.1-20d4d96.tgz
https://rw-pr-redwoodjs-com.s3.amazonaws.com/1624/redwoodjs-core-0.22.1-20d4d96.tgz
https://rw-pr-redwoodjs-com.s3.amazonaws.com/1624/redwoodjs-dev-server-0.22.1-20d4d96.tgz
https://rw-pr-redwoodjs-com.s3.amazonaws.com/1624/redwoodjs-eslint-config-0.22.1-20d4d96.tgz
https://rw-pr-redwoodjs-com.s3.amazonaws.com/1624/redwoodjs-eslint-plugin-redwood-0.22.1-20d4d96.tgz
https://rw-pr-redwoodjs-com.s3.amazonaws.com/1624/redwoodjs-forms-0.22.1-20d4d96.tgz
https://rw-pr-redwoodjs-com.s3.amazonaws.com/1624/redwoodjs-internal-0.22.1-20d4d96.tgz
https://rw-pr-redwoodjs-com.s3.amazonaws.com/1624/redwoodjs-router-0.22.1-20d4d96.tgz
https://rw-pr-redwoodjs-com.s3.amazonaws.com/1624/redwoodjs-structure-0.22.1-20d4d96.tgz
https://rw-pr-redwoodjs-com.s3.amazonaws.com/1624/redwoodjs-testing-0.22.1-20d4d96.tgz
https://rw-pr-redwoodjs-com.s3.amazonaws.com/1624/redwoodjs-web-0.22.1-20d4d96.tgz

Install this PR by running yarn rw upgrade --pr 1624:0.22.1-20d4d96

[peterp]

Aaaah, the best code is almost no code.