Knocking feature polishing part 2 (#3738)

* improved implementation of the unknown state

* forget button in the banned state

* error handling for forbidden access

* added the forget function

fixed DMs, and updated preview tests

* removed banned room proxy

* code polishing and test improvement

ElementX/Sources/Services/Room/RoomPreview/RoomPreviewProxyProtocol.swift

@@ -11,4 +11,7 @@ import Foundation
 protocol RoomPreviewProxyProtocol {
     var info: RoomPreviewInfoProxy { get }
     var ownMembershipDetails: RoomMembershipDetailsProxyProtocol? { get async }
+    
+    /// Use this function to forget the room, should only be used if the current user membership is `banned`
+    func forgetRoom() async -> Result<Void, RoomProxyError>
 }