Introduce LeaderboardSubmissionButton widget

Added a new LeaderboardSubmissionButton widget to facilitate user submissions to the leaderboard. The button is styled consistently with other application buttons and features an emoji trophy icon to indicate leaderboard submissions. It provides a mechanism for disabling submissions based on certain conditions.

frontend/lib/views/task_queue/leaderboard_submission_button.dart

@@ -0,0 +1,48 @@
+import 'package:auto_gpt_flutter_client/constants/app_colors.dart';
+import 'package:flutter/material.dart';
+
+class LeaderboardSubmissionButton extends StatelessWidget {
+  final VoidCallback? onPressed;
+  final bool isDisabled;
+
+  LeaderboardSubmissionButton(
+      {required this.onPressed, this.isDisabled = false});
+
+  @override
+  Widget build(BuildContext context) {
+    return SizedBox(
+      height: 50,
+      child: ElevatedButton(
+        style: ElevatedButton.styleFrom(
+          backgroundColor: isDisabled ? Colors.grey : AppColors.primaryLight,
+          shape: RoundedRectangleBorder(
+            borderRadius: BorderRadius.circular(8.0),
+          ),
+          padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
+          elevation: 5.0,
+        ),
+        onPressed: isDisabled ? null : onPressed,
+        child: const Row(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: [
+            Text(
+              'Submit to leaderboard',
+              style: TextStyle(
+                color: Colors.white,
+                fontSize: 12.50,
+                fontFamily: 'Archivo',
+                fontWeight: FontWeight.w400,
+              ),
+            ),
+            SizedBox(width: 10),
+            Icon(
+              Icons.emoji_events,
+              color: Colors.white,
+              size: 24,
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}