Description
Allow setting some default options at the message level in config/packages/mailer.yaml. Suggestions:

• from: The way suggested at https://symfony.com/doc/master/mailer.html#email-addresses (event subscriber) seems (a) cumbersome and (b) inflexible (what if I want the ability to override the default from in some cases?)
• headers: The X-Auto-Response-Suppress header explained at https://symfony.com/doc/master/mailer.html#message-headers would be a good candidate