fix: only append 'Elastic/Synthetics' to default UA

[andrewvc]

When we originally implemented #232 it appears we didn't implement the third AC, allowing users to override our custom UA string "Elastic/Synthetics" which is appended.

Some users need to fully replace the UA, this allows them to do that. Rather than adding a boolean, this assumes that if you're overriding the UA you want full control, which is more in line with the principle of least surprise.

CC @paulb-elastic @drewpost

PS this is currently a draft because there are no tests, I'll add tests if we agree on this approach.

[apmmachine]

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• Start Time: 2022-06-03T00:23:25.513+0000

• Duration: 15 min 30 sec

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Total	166

🤖 GitHub comments

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[vigneshshanmugam]

@andrewvc Should be good to go after we fix the tests.

[justinkambic]

Post-FF testing LGTM:

I set up a project like:

// synthetics.config.js
const config = {
  playwrightOptions: {
    userAgent: "DO NOT SAY ELASTIC",
  },
};

module.exports = config;

// test.journey.ts
const { journey, step, expect } = require('@elastic/synthetics');

journey(
  { name: 'Test', tags: ['browse'] },
  ({ page, params }) => {

    step('go to my untrusted HTTPS endpoint', async () => {
      await page.goto('https://www.whatismybrowser.com/');
      await new Promise(r => setTimeout(r, 50000));
    });
  }
);

When running the journey, I got the following output:

[shahzad31]

POST FF Testing looks good !!