Fill issue_id column when creating test reports

Populate test_reports.issue_id when creating a new test report with the parent requirement associated issue id.

In ruby words, after creating a requirement we should:

test_report.issue_id = test_report.requirement.requirement_issue.id

To achieve this we need to remove requirements_test_reports_requirement_id_xor_issue_id constraint
which allows only issue_id or requirement_id being present. After removing the constraint we should populate both issue_id and requirement_id.

The old requirement_id association will be removed on #345845 (closed).