Added DeepL API key setting

I18N Commander/UI WinForms/Components/Setting.cs

@@ -45,7 +45,7 @@ public partial class Setting : UserControl
         Func<Control> SetupDataControl
     );
 
-    private static async Task<Setting> ShowDeepLSettingAsync()
+    private static async Task<Setting> ShowDeepLModeSettingAsync()
     {
         var currentSetting = await AppSettings.GetDeepLMode();
         var settingData = new SettingUIData(
@@ -91,8 +91,32 @@ public partial class Setting : UserControl
         };
     }
     
+    private static async Task<Setting> ShowDeepLAPIKeySettingAsync()
+    {
+        var currentSetting = await AppSettings.GetDeepLAPIKey();
+        var settingData = new SettingUIData(
+            Icon: Icons.icons8_key_512,
+            SettingName: () => "DeepL API Key",
+            SettingExplanation: () => "The API key is required to use the DeepL translation service. You can find your API key on the DeepL website.",
+            SetupDataControl: () =>
+            {
+                var textbox = new TextBox();
+                textbox.Text = currentSetting;
+                textbox.TextChanged += async (sender, args) => await AppSettings.SetDeepLAPIKey(textbox.Text);
+                textbox.Dock = DockStyle.Fill;
+                return textbox;
+            }
+        );
+
+        return new Setting(settingData)
+        {
+            Dock = DockStyle.Top,
+        };
+    }
+
     public static IEnumerable<Task<Setting>> GetAllSettings()
     {
-        yield return ShowDeepLSettingAsync();
+        yield return ShowDeepLAPIKeySettingAsync();
+        yield return ShowDeepLModeSettingAsync();
     }
 }