Add attchment support to SendGridAdapter
Summary:
- Add attachment support for SendGrid.
- Add attachment support to the MetaMTA test console.
Test Plan:
- Sent myself a file with Amazon SES via test console.
- Sent myself a file with SendGrid via test console.
Reviewers: mareksapota, jungejason, nh, tuomaspelkonen, aran
Reviewed By: jungejason
CC: aran, jungejason
Differential Revision: 1089