Added lastname.firstname as email format

[snipe]

Fixes #14918 - this adds lastname.firstname as a format for email/usernames.

[what-the-diff]

PR Summary

• Adjustment to User Name Formatting Approach in Application
  A new rule has been implemented inside the application's User model. This rule changes the way user names are generated when a certain format, specifically 'lastname.firstname', is used. This enables the user names to better correspond to this chosen format.

• Added New Localization Key
  A new language localization key has been added - 'lastnamefirstname'. This is for supporting our multi-lingual user base. It is associated with the descriptive value 'Last Name First Name ([email protected])', which will be used as a template for presenting user names.

• Inclusion of New Option into Macro Array
  An additional option, 'lastname.firstname', has been inserted into the application's macro array. This references the new localization key and is crucial in ensuring our application caters to diverse user naming conventions.