Store "other recipients" in mongodb thread object

[khakers]

Is your feature request related to a problem? Please elaborate.

Other recipients (all those added to a thread aside the creator) are currently only stored within the topic of a channel. This makes them difficult to parse and also means it's easy to accidently break the state, especially if a user reasonably assume that channels do not store actual bot state. It also means that it's impossible to check who the "other recipients" were after a thread has been closed.

Describe the solution you'd like

Store other recipients within mongodb. When retrieving recipients, use the values stored for the thread within the database instead of checking the topic or genesis message.

Does your solution involve any of the following?

• Logviewer
• New config option

Describe alternatives you've considered

maintain status quo, stops progress towards removing reliance on channel names and topics, and improving resiliency.

Who will this benefit?

Will benefit all users by reducing the dependence of modmail on easily changed discord based information that requires fragile string parsing. Will benefit historical threads by allowing users to see all the users that were added to a thread.

Additional Information

No response