ses/domain: DMARC reports handler

[mskrajnowski]

Would be nice to add automated handling of DMARC reports. We could do that by adding a subdomain for incomming emails and a lambda function which would store the reports in an S3 bucket, parse them and publish the results as cloudwatch metrics so we can easily check them and create alarms with them.

[mskrajnowski]

https://pypi.org/project/parsedmarc/