JUnit XML should have `timestamp` attrubute

[evrom]

🤔 What's the problem you're trying to solve?

Looking at a report, the viewer doesn't know when the tests were executed. This makes it impossible to know if the report is recent or relevant if only the report is available.

✨ What's your proposed solution?

Add timestamp as an attribute to the testsuite element. It is supported by other test reporting libraries using the JUnit.xml format.

⛏ Have you considered any alternatives or workarounds?

A workaround is a custom script that runs the tests, which can store a timestamp before starting the tests, and then add the timestamp to the report.

📚 Any additional context?

No response

[davidjgoss]

Thanks for raising @evrom and doubly so for taking the time to make the PR in cucumber-js.

I've transferred your issue because we're currently replacing that formatter with the one produced by this repo (via #42) for consistency across different language implementations of Cucumber.

We can certainly consider the inclusion of timestamp here - cc @mpkorstanje

[mpkorstanje]

While the timestamp is not in original XSD for JUnit, it does look like it is a common enough property. So I reckon we can support it without breaking anything.

We'll have to update the README to say something to that effect though.