Improve email preferences

[MJGaughran]

This is for the Codeathon task: https://github.com/ControlSystemStudio/phoebus-codeathon/tree/master/projects#phoebus-ui-005-default-email-address-preferences

There are a couple of differences to that project description:

• Preference is labelled 'to', in line with the existing 'from' field
• Username macro would be 'user.name' since it uses the system properties

Checklist

• Testing:

  • The feature has automated tests
  • Tests were run
  • If not, explain how you tested your changes

• Documentation:

  • The feature is documented
  • The documentation is up to date
  • Release notes:
    • Added an entry if the change is breaking or significant
    • Added an entry when adding a new feature

[sonarqubecloud]

Quality Gate passed

Issues
4 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 SonarQube Cloud

[shroffk]

@GDH-ISIS @Monarda can you have a look #3589