Add `BASE_URL` support

When you have multiple environments you might want to run your tests with different base URLs for each environment. For example:

BASE_URL=http://www.staging.your-awesome-application.com npx @puppeteer/replay recording.json

BASE_URL=http://www.test.your-awesome-application.com npx @puppeteer/replay recording.json

[OrKoN]

@puskuruk I think it’d be nice to allow importing custom runner extensions so that use case/app-specific logic could be implemented. But I think it’s something that we need to take a look into!

[puskuruk]

Since we have a solution to modify URLs with an extension we can close this issue. 🙏

Example implementation:

const { PuppeteerRunnerExtension } = require('@puppeteer/replay')

class Extension extends PuppeteerRunnerExtension {
  async runStep(step, flow) {
    if ('url' in step) {
      // modify URL here
      // reassign step here
    }

    await super.runStep(step, flow)
  }
}