attachment from a forwarded encrypted contact page message becomes unavailable (todo: update contact page to use pgp/mime for attachments)

[martgil]

Scenario:
A user receives a secure email with an attachment from ECP and forwards the said email to a friend, the attachment from the ECP message is not included in the forwarded email received by the recipient (only the text is visible).

Steps to reproduce:
user 1 - sender
user 2 - receiver

1. User 1 has ECP configured.
2. User 1 receives a message with an attachment from ECP
3. User 1 forwarded the said message to User 2
4. User 2 only receives the message but not the attached file.

Reference: https://mail.google.com/mail/u/human@flowcrypt.com/#inbox/FMfcgzGrbbwWxctDmMRxWxpFZXPNqrpp

[tomholub]

We should switch ECP to start using pgp/mime attachments. After that, re-triage this issue. I expect it should get resolved.