Assign feedback when closing a conversation

[ruKurz]

Current state
When closing a conversation, the user is informed that conversation is now closed.

Preferred state
When closing a conversation, the user is asked for feedback: "War die Konversation hilfreich? - Ja/Nein" ("Was the conversation helpful? - Yes / No")

mrsimpson#74

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.