[MM-12667] Allow including deactivated users in bulk import and export (#10353)

* [MM-12667] Allow including deactivated users in bulk import and export

1. Added `deleteAt` for user type import line
2. Adding deactivated users data in bulk export
3. Importing deactivated users data in bulk import

Added/Updated relevant test cases

* Fixed export of replies to posts by deleted users.
Updated tests for same

app/import_functions.go

@@ -369,6 +369,13 @@ func (a *App) ImportUser(data *UserImportData, dryRun bool) *model.AppError {
 		}
 	}
 
+	if data.DeleteAt != nil {
+		if user.DeleteAt != *data.DeleteAt {
+			user.DeleteAt = *data.DeleteAt
+			hasUserChanged = true
+		}
+	}
+
 	var roles string
 	if data.Roles != nil {
 		if user.Roles != *data.Roles {