4724: Optional usage DEFAULT_FROM_EMAIL for request mails

Tab10id

What version are you running?

3.0.8

Describe the enhancement and the motivation for it.

Our smtp server prevent sending mails with different sender mail (argument from_email of EmailMessage) and allow only own account for this field

Please provide any additional information below.

https://github.com/reviewboard/reviewboard/blob/dd97c294ee1bac369b2b0ee3425054db0a8f730f/reviewboard/notifications/email/message.py#L236
That line use mail of review/request user.
For now we change this line to from_email=settings.DEFAULT_FROM_EMAIL
but we want to have option for this in admin panel.