fix: Cleanup S3 Attachments (#1217)

* fix: Server error if attempting to load an unknown attachment

* fix: Migration should cascade delete to document attachments

* fix: Delete S3 attachments along with documents

server/models/Attachment.js

@@ -1,6 +1,7 @@
 // @flow
 import path from 'path';
 import { DataTypes, sequelize } from '../sequelize';
+import { deleteFromS3 } from '../utils/s3';
 
 const Attachment = sequelize.define(
   'attachment',
@@ -50,6 +51,10 @@ const Attachment = sequelize.define(
   }
 );
 
+Attachment.beforeDestroy(async model => {
+  await deleteFromS3(model.key);
+});
+
 Attachment.associate = models => {
   Attachment.belongsTo(models.Team);
   Attachment.belongsTo(models.Document);