feat: add close button for pause selection dialog

packages/flutter_availability/lib/src/ui/widgets/pause_selection.dart

@@ -296,7 +296,9 @@ class _AvailabilityBreakSelectionDialogState
         ? translations.pauseDialogDescriptionTemplate
         : translations.pauseDialogDescriptionAvailability;
 
-    return Container(
+    return Stack(
+      children: [
+        Container(
           margin: EdgeInsets.symmetric(
             horizontal: spacing.sidePadding,
           ),
@@ -349,6 +351,17 @@ class _AvailabilityBreakSelectionDialogState
               ],
             ),
           ),
+        ),
+        Positioned(
+          right: 0,
+          top: 0,
+          child: IconButton(
+            padding: const EdgeInsets.all(16),
+            icon: const Icon(Icons.close),
+            onPressed: () => Navigator.of(context).pop(),
+          ),
+        ),
+      ],
     );
   }
 }