generateEmailMessage() instead of generateEmailHTML() and generateEmailSubject()

[berndb]

in our payload project we send a lot of different emails.

we have a helper class which renders all the different emails and return Message instances which can then be passed to payload. sendEmail(message: Message).

however for the verify and forgotPassword configuration, we cannot return a Message instance. instead, we have to rip the message apart into a function which returns the subject and another function which returns the html.

it currently looks like this:

    verify: {
      generateEmailHTML: ({ req, token, user }) => {
        const message = getEmailService().createUserWelcomeEmail(token, user)
        return message.html
      },
      generateEmailSubject: ({ req, token, user }) => {
        const message = getEmailService().createUserWelcomeEmail(token, user)
        return message.subject
      },
    },

it would be nice to have the option to configure a generateEmailMessage function which accepts a Message instance as return value:

    verify: {
      generateEmailMessage: ({ req, token, user }) => {
        const message: Message = getEmailService().createUserWelcomeEmail(token, user)
        return message
      }
    },

This way, it would be more efficient because the messages would not have to be rendered twice and it would also be possible to return a different from address instead of the default from address. (and maybe even all other attributes supported by Nodemailer, like attachments, plain text, etc.)