fix #19: Sort CSV field names prior to export

[mbhutton]

This is to achieve a stable column order for CSV exports, as the order in which CSV fields are discovered is influenced by the order of the tasks, as tasks can have differing sets of fields.

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[AlexanderWillner]

Thank you