bug(attachments): Prevent duplicate attachments from being indexed in forwarded emails

[junaid-shirur]

Duplicate attachments are being indexed when emails are forwarded within a thread. We need to implement a solution to prevent this while ensuring proper access to attachments.

Issue Details:

• When an email is forwarded, its attachments may get duplicated.
• For non-forwarded emails, we can use the threadId to check if an attachment already exists in the thread.
• For forwarded emails, we still need to index the attachments but may need to adjust their permissions to ensure that other recipients can still access them
• If a forwarded email includes new attachments, should we rely on the filename to differentiate them?