New Server Configuration to Avoid Saving Email Content

[anselmobattisti]

Currently, the Postal server allows configuring the retention period for HTML bodies, plain text, and attachments. However, there is no option to completely disable the storage of email content.

It would be highly beneficial to introduce a configuration setting that allows the server to store only metadata (such as sender, recipient, subject, timestamps, etc.) while discarding the actual content of the messages (body and attachments) immediately upon receipt.

This feature would be particularly useful for environments with strict privacy or compliance requirements, or where message content is not needed after delivery.

This request is similar to https://github.com/orgs/postalserver/discussions/3367 however to completly disable this feature in the system.