Let jest-playwright.config.js export an async function

[thernstig]

Is your feature request related to a problem? Please describe.
I want to use async/await in my jest-playwright.config.js as it is nicer and easier to read code that way.

Describe the solution you'd like
Similar to how Jest's globalSetup can except the export of an async function, so should the above config like:

module.exports = async () => {
  // Do some cool async stuff here
  if (foo) {
    await exec('foominator', {
      cwd: path.join(repoRoot, 'clientclient'),
    });
  }
};

[thernstig]

@mmarkelov it would be good if the README was updated to state that this is supported?