Added SES attachments support

[galezra]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  Feature request: SES attachments support #98

• What is the current behavior? (You can also link to an open issue here)
  No support for file attachments.

• What is the new behavior (if this is a feature change)?
  SES provider now supports attachments.

• Other information:
  The feature hasn't been tested yet, we need to validate the transporter through nodemailer

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[scopsy]

@galezra the nodemailer approach just wasn't working for me :(

Replace it with email.js to generate the raw message and used the aws-ses, not the v2 one. Tested it locally with a valid SES key and seems to work 🎉

Let me know what you think

[galezra]

It looks awesome! 3.0 🙌🏼