Add goal field to update/create sprint

[zbarahal]

https://github.com/pycontribs/jira/pull/1586 seems like it stalled out after you asked for tests so I created a separate PR.

This adds goal as a field to create/update sprint and adds test cases. There weren't any existing test cases for update_sprint so I extended that.

I'm still working on getting the local dev setup but I figure I can see how the tests run in CI