feat: Add duplicate finder script to find duplicates on any table (#1781)

* Create readme.md

* Create script.js which finds duplicates

* Update readme.md

* Update script.js

* Update readme.md

* Update script.js to work on inherited fields

Author: JohanDC-1999

Server-Side Components/Background Scripts/Duplicate Finder/readme.md

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+## ServiceNow Duplicate Record Finder
+A simple server-side script for ServiceNow that finds and reports on duplicate values for any field on any table. It uses an efficient GlideAggregate query and formats the results into a clean, readable report.
+
+### How to Use
+This script is designed to be run in **Scripts - Background** or as a Fix Script.
+1. Navigate: Go to **System Definition > Scripts - Background** (or type sys.scripts.do in the filter navigator).
+2. Copy Script: Copy the entire contents of the script.js file.
+3. Paste and Configure: Paste the script into the "Run script" text box. Add the table to search in `tableName` and the field to search for duplicates in `fieldName`
+  ```js
+  // Update ONLY below values to find duplicates
+  var tableName = '<table_name>'; // ADD: Table you want for duplicates
+  var fieldName = 'field_name';	// ADD: Field that you want to check for duplicates
+  ```
+  For example, to find duplicate email addresses in the User table:
+  ```js
+  var tableName = 'sys_user';
+  var fieldName = 'email';;
+  ```
+  To find incidents with the same short description:
+  ```js
+  var tableName = 'incident';
+  var fieldName = 'short_description';
+  ```
+
+
+4. Run Script: Click the "Run script" button. The results will be displayed on the screen below the editor.
+

Server-Side Components/Background Scripts/Duplicate Finder/script.js

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+// Update ONLY below values to find duplicates
+var tableName = 'incident'; // ADD: Table you want for duplicates
+var fieldName = 'short_description';	// ADD: Field that you want to check for duplicates
+
+findDuplicates(tableName, fieldName);
+
+function findDuplicates(tableName, fieldName) {
+    /**************************************/
+    /*** Basic error handling on inputs ***/
+    /**************************************/
+
+    // Check if table exists
+    if (!gs.tableExists(tableName)) {
+        // MODIFIED: Switched to string concatenation
+        gs.info('Table "' + tableName + '" does not exist.');
+        return;
+    }
+
+    // Check if field exists
+    var gr = new GlideRecord(tableName);
+    gr.initialize();
+    if (!gr.isValidField(fieldName)) {
+        gs.print('No field called "' + fieldName + '" on the "' + tableName + '" table.');
+        return;
+    }
+
+    /***************************************/
+    /*********** Find duplicates ***********/
+    /***************************************/
+    var duplicateJson = {}; // Store the duplicate records
+    var duplicateGroupCount = 0; // Counts the number of groups of duplicates
+
+    var duplicateAggregate = new GlideAggregate(tableName);
+    duplicateAggregate.addAggregate('COUNT', fieldName);
+    duplicateAggregate.groupBy(fieldName);
+    duplicateAggregate.addHaving('COUNT', '>', 1); // More than 1 means it is a duplicate
+    duplicateAggregate.addNotNullQuery(fieldName); // Ignore records where the field is empty
+    duplicateAggregate.query();
+
+    while (duplicateAggregate.next()) {
+        duplicateGroupCount++;
+        var fieldValue = duplicateAggregate.getValue(fieldName);
+        var countInGroup = duplicateAggregate.getAggregate('COUNT', fieldName);
+        duplicateJson[fieldValue] = countInGroup;
+    }
+
+    /***************************************/
+    /********** Print the results **********/
+    /***************************************/
+
+    // No duplicates found
+    if (Object.keys(duplicateJson).length === 0) {
+        gs.print('No duplicates found for field "' + fieldName + '" on table "' + tableName + '".');
+        return;
+    }
+
+    // Duplicates were found
+    gs.print("Found " + duplicateGroupCount + " groups of duplicates:");
+    
+    for (var key in duplicateJson) {
+        gs.print('Value "' + key + '" has ' + duplicateJson[key] + ' occurrences.');
+    }
+}
+