Feature: Add 'Email all' button to Users tab to send email to all users

[cmyers-mieweb]

Feature Request

In the 'Users' tab, add a button next to the existing 'Invite' and 'New User' buttons labeled "Email all". When clicked, this button should:

1. Open a modal or popup with:
   • A required Subject field
   • A required Message field
2. Upon completion and submission:
   • An email is sent from the opensource-server to all users in the current users list.

Why?
This will allow admins to quickly send an email to all registered users directly from the user interface, improving communication and workflow.

Acceptance Criteria:

• The 'Email all' button appears next to 'Invite' and 'New User' in the Users tab.
• Modal includes Subject and Message fields (both required).
• Submitting form sends an email to all users through the opensource-server's email system.
• Proper error handling for failed emails.

Additional Notes:

• Please consider confirmation before sending the email.
• Ensure only authorized users (admins) can access this functionality.
• UI/UX should align with current tab style.