Added optional owner-attribute for testcase

[work933k]

This PR proposes to add support for defining the owner-attribute of testcase.
This attribute is used by Azure Devops' PublishTestResult-task

This should be a non-breaking change as the ownerName is optional.

[palmerj3]

Thanks for submitting a PR!

I need to do some work on the CI here before I'll be able to merge.

For this feature, I would like you to consider enabling different owners for different tests. Your approach assumes a single owner for an entire suite.

Have a look what we did to support custom test suite properties and an approach similar to that might be justified.

https://github.com/jest-community/jest-junit/blob/master/utils/buildJsonResults.js#L158

[work933k]

Thank you for your quick response.

I understand your suggestion to support different owners for different tests. But maybe it would be a good to initially start small/easy with this implementation?

[palmerj3]

Since you're adding a config / cli arg to specify the owner, if we move to multi-owner later on then that config goes away. Could be avoided altogether.