[Feature]: add --fail-on-flaky-tests in config file

[jfgreffier]

🚀 Feature Request

I would like to have an failOnFlakyTests option in playwright.config.ts rather than only in CLI. Its default value should be false.

Example

export default defineConfig({
  testDir: './tests',
  /* Run tests in files in parallel */
  fullyParallel: true,
  /* Fail the build on CI if you accidentally left test.only in the source code. */
  forbidOnly: !!process.env.CI,
  /* Retry on CI only */
  retries: process.env.CI ? 2 : 0,
+++  /* Don't accept flaky tests */
+++  failOnFlakyTests: process.env.CI ? true : false,

Motivation

We probably don't want the same settings in CI and locally.
I feel it's more a configuration point than something that you would use occasionally. Really similar to forbidOnly