Email Notification Improvements

[kingzacko1]

Description

• Adds option to send notification as a single email instead of one per recipient
• Adds option to add users/emails to the email CC line
• Adds option to add users/emails to the email BCC line

Motivation and Context

• Gives users more control over how email notifications are sent.
• Allows notification recipients to more clearly differentiate intended primary recipients vs secondary
• Closes Support CCs in Email Notifications #20809

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[danotorrey]

@kingzacko1 Sorry for the delay. I'll review this ASAP.