Export and import hide_notifications alongside user mutes (#10335)

* Export hide_notifications along with user mutes

* Import hide_notifications along with muted users list

* Add headers for CSV exports

app/models/export.rb

@@ -14,7 +14,11 @@ class Export
   end
 
   def to_muted_accounts_csv
-    to_csv account.muting.select(:username, :domain)
+    CSV.generate(headers: ['Account address', 'Hide notifications'], write_headers: true) do |csv|
+      account.mute_relationships.includes(:target_account).reorder(id: :desc).each do |mute|
+        csv << [acct(mute.target_account), mute.hide_notifications]
+      end
+    end
   end
 
   def to_following_accounts_csv