Metadata status changes notification mails improvements

[josegar74]

1. Don't add saludation if the user to notify is the catalogue administrator (defined in settings), as only has the email address.

Test case:

• Update the notification level in the database for DOI request to catalogueAdministrator

  UPDATE StatusValues SET notificationLevel = 'catalogueAdministrator' WHERE name = 'doiCreationTask';
  

• Configure the DOI server in the settings and the mail configuration.

• Create a new metadata and publish it.

• Request the DOI.

  • Without the fix: the mail start with a placeholder for the username:

    {{userName}},
    ... requested creation of the DOI for the record...
    

  • With the fix:

    ... requested creation of the DOI for the record...
    

2. Filter out the users without mail when retrieving the users to notify.

Checklist

• [X] I have read the contribution guidelines
• [X] Pull request provided for main branch, backports managed with label
• [ ] Good housekeeping of code, cleaning up comments, tests, and documentation
• [X] Clean commit history broken into understandable chucks, avoiding big commits with hundreds of files, cautious of reformatting and whitespace changes
• [X] Clean commit messages, longer verbose messages are encouraged
• [ ] API Changes are identified in commit messages
• [ ] Testing provided for features or enhancements using automatic tests
• [ ] User documentation provided for new features or enhancements in manual
• [ ] Build documentation provided for development instructions in README.md files
• [ ] Library management using pom.xml dependency management. Update build documentation with intended library use and library tutorials or documentation