MM-11782: Make archived channels experimental and off-by-default. (#9281)

* MM-11782: Make archived channels experimental and off-by-default.

* Fix test.

model/config.go

@@ -1125,7 +1125,7 @@ type TeamSettings struct {
 	MaxNotificationsPerChannel          *int64
 	EnableConfirmNotificationsToChannel *bool
 	TeammateNameDisplay                 *string
-	ViewArchivedChannels                *bool
+	ExperimentalViewArchivedChannels    *bool
 	ExperimentalEnableAutomaticReplies  *bool
 	ExperimentalHideTownSquareinLHS     *bool
 	ExperimentalTownSquareIsReadOnly    *bool
@@ -1255,8 +1255,8 @@ func (s *TeamSettings) SetDefaults() {
 		s.EnableUserCreation = NewBool(true)
 	}
 
-	if s.ViewArchivedChannels == nil {
-		s.ViewArchivedChannels = NewBool(true)
+	if s.ExperimentalViewArchivedChannels == nil {
+		s.ExperimentalViewArchivedChannels = NewBool(false)
 	}
 }