Get issue labels.
        :param issue_key:
        :return:

def get_issue_labels(self, issue_key):
        """
        Get issue labels.
        :param issue_key:
        :return:
        """
        url = 'rest/api/2/issue/{issue_key}?fields=labels'.format(issue_key=issue_key)
        return (self.get(url) or {}).get('fields').get('labels')