As a user, I can add Tests when creating a Test Execution issue

When creating a Test Execution issue, the user should be able to choose the initial Tests or Test Sets to associate with the Test Execution.

This must be achieved with the "Tests association with a Test Execution" custom field. This custom field must provide a select dropbox similar to the "Test Sets association with a Test" custom field in the create/edit Test issue screen.

Here, the user can select Test or Test Set issues to associate. When the issue is created, all selected Tests either directly or indirectly through Test Sets must be added to the Test Execution.

This custom field will not be provided in Test Execution edit screen as it may contain a high number of Tests that could affecting usability as well as performance. If the Test Execution does not have any Tests yet then this custom field will be present as in the create issue screen.