Add support for attachments in Email mapper

[potiuk]

Is your feature request related to a problem? Please describe.
Email action can send emails with attachments but it's rather difficult to have the attachments exchanged between DataProc and Airflow node. It's possible but complex to get it right. This is rather obscure feature and we think it can be rather easily workarounded manually after conversion process finishes but when not only Dataproc is supported, we should possibly add this capability

Describe the solution you'd like
Attachments should be possible to send via Email Action.