Test issues must be created automatically when importing execution results using the Xray JSON format

Currently, the Xray JSON format does not automatically create Test issues. When importing execution results, the Test issues must already exist. 

The Xray JSON format must also support creating new Test cases, in case these do not exist in Jira. This must be valid for any Test Type. For this, the schema must be changed in order to support another way of identifying test cases (besides the issue key), and also providing new Test definitions for Manual, Gherkin, and Unstructured Tests.