feat: Add Instance Details ViewModel and UI for managing instance credentials

- Introduced InstanceDetailsViewModel to handle loading and displaying instance-specific credentials.
- Created InstanceDetailsWindow and associated XAML for displaying admin, database, and OAuth2 credentials.
- Updated InstancesViewModel to include command for opening instance details.
- Enhanced SettingsViewModel to manage Bitwarden and Xibo Bootstrap configurations, including connection testing.
- Added UI components for Bitwarden Secrets Manager and Xibo Bootstrap OAuth2 settings in the SettingsView.
- Implemented password visibility toggles and clipboard copy functionality for sensitive information.

OTSSignsOrchestrator.Desktop/Views/InstanceDetailsWindow.axaml.cs

@@ -0,0 +1,11 @@
+using Avalonia.Controls;
+
+namespace OTSSignsOrchestrator.Desktop.Views;
+
+public partial class InstanceDetailsWindow : Window
+{
+    public InstanceDetailsWindow()
+    {
+        InitializeComponent();
+    }
+}