Multiple correspondent fields: sender, recipients, CC, BCC

[catleeball]

Issue

Right now, Paperless-ng seems to support only one Correspondent per document. The docs define this as:

The correspondent of a document is the person, institution or company that a
document either originates form, or is sent to.

This indicates that the user should pick correspondent to mean either sender or receiver, and be consistent with this.

Feature Request

It would be nice if Correspondent was instead multiple fields, such as:

• Sender
• Recipients
• CCed
• BCCed

This better matches how documents are corresponded via mail or email, and allows for more granular and definite matching.

Example Use Cases

• A bank statement mailed to a couple with a joint account
  • Sender: Bank Corp
  • Recipients: Randy Jones, Martha Jones
• A landlord mails a notice to multiple roommates in an apartment
  • Sender: Joe Scumbo
  • Recipients: Benny, Denny, Manny, Danny, Bob
• An important email from a thread of emails is archived as a PDF
  • Sender (FROM line): "Satoshi Morimoto <[email protected]>"
  • Recipients (TO line): "[email protected]"
  • CC: "[email protected]", "Juan Rodriguez <[email protected]>"
  • BCC: "Lenny Jones <[email protected]>"