Announcement banner (#2205)

* Create annoucement_banner.js

* Create README.md

Author: MYaswanth28

Client-Side Components/UI Scripts/PersistentAnnouncementBanner/README.md

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+This UI Script is used to inject a custom, highly visible, and persistent notification banner across the top of the entire ServiceNow platform interface. 
+
+It is ideal for communicating critical, non-transactional system messages such as scheduled maintenance, major outages, or company-wide policy announcements.
+
+The key feature of this banner is that it is dismissible, and it uses a User Preference to ensure that once a user closes a specific version of the announcement
+
+The Reason to use this is , Announcements Banner Module Sometimes Loads Slower or Doesnt trigger the notification banner , instead this scripts all the time,if user is logged in 

Client-Side Components/UI Scripts/PersistentAnnouncementBanner/annoucement_banner.js

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+(function() {
+    var BANNER_TEXT = ' **SYSTEM ALERT:** Scheduled maintenance for all services will occur this Saturday from 1 AM to 4 AM UTC. Expect minor downtime. 🚨';
+    var BANNER_BG_COLOR = '#ffcc00'; // Warning yellow
+    var BANNER_TEXT_COLOR = '#333333';
+
+    // Check if the user has already dismissed this version of the banner
+    var isDismissed = (g_preference.get(PREF_KEY) === 'true');
+
+    if (isDismissed) {
+        return;
+    }
+    var banner = document.createElement('div');
+    banner.setAttribute('id', 'global_announcement_banner');
+    banner.innerHTML = BANNER_TEXT;
+    banner.style.cssText = [
+        'position: fixed;',
+        'top: 0;',
+        'left: 0;',
+        'width: 100%;',
+        'padding: 10px 40px 10px 15px;', // Added padding on the right for the close button
+        'background-color: ' + BANNER_BG_COLOR + ';',
+        'color: ' + BANNER_TEXT_COLOR + ';',
+        'z-index: 10000;', // High z-index to ensure it sits on top of everything
+        'text-align: center;',
+        'font-weight: bold;',
+        'box-shadow: 0 2px 5px rgba(0,0,0,0.2);'
+    ].join('');
+    var closeButton = document.createElement('span');
+    closeButton.innerHTML = '×'; // Times symbol
+    closeButton.style.cssText = [
+        'position: absolute;',
+        'top: 50%;',
+        'right: 15px;',
+        'transform: translateY(-50%);',
+        'font-size: 20px;',
+        'cursor: pointer;',
+        'font-weight: normal;',
+        'line-height: 1;'
+    ].join('');
+
+    closeButton.onclick = function() {
+        // Remove the banner from the DOM
+        banner.remove(); 
+        
+        // Set the User Preference so the banner stays dismissed across sessions
+        g_preference.set(PREF_KEY, 'true');
+    };
+    banner.appendChild(closeButton);
+    document.body.appendChild(banner);
+
+})();