Transform Map - Prevent Priority Update unless on Insert - Pull 1 (#2365)

* Add README for Incident Priority Set on Insert Only

Added documentation for the Incident Priority Set on Insert Only script, explaining its purpose, usage, and functionality.

* Add insert-only priority setting script

Implement onBefore script to set priority during insert operations based on impact and urgency.

Author: hanna-g-sn

Server-Side Components/Transform Map Scripts/Incident Priority Set on Insert Only/README.md

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+# Incident priority set on insert only
+
+## What this solves
+Recurring imports often overwrite priority even after the service desk has triaged the ticket. This onBefore script sets priority only when a row is inserted. Updates pass through without touching priority.
+
+## Where to use
+Attach to your Incident Transform Map as an onBefore script.
+
+## How it works
+- Checks the Transform Map action variable for insert vs update
+- On insert, computes priority from impact and urgency
+- On update, does nothing to priority
+
+## References
+- Transform Map scripts  
+  https://www.servicenow.com/docs/bundle/zurich-integrate-applications/page/administer/import-sets/task/t_AddOnBeforeScriptToTransformMap.html
+- Incident fields and priority logic  
+  https://www.servicenow.com/docs/bundle/zurich-it-service-management/page/product/incident-management/concept/incident-fields.html

Server-Side Components/Transform Map Scripts/Incident Priority Set on Insert Only/onBefore_set_priority_insert_only.js

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+// Transform Map onBefore script: set priority on insert, not on update
+(function runTransformScript(source, map, log, target) {
+  try {
+    if (String(action).toLowerCase() !== 'insert') {
+      log.info('Priority unchanged on update for number: ' + (target.number || '(new)'));
+      return;
+    }
+
+    var impact = Number(source.impact) || 3;   // 1..3 typical
+    var urgency = Number(source.urgency) || 3; // 1..3 typical
+
+    // Simple matrix: priority = impact + urgency - 1, clamped 1..5
+    var p = Math.max(1, Math.min(5, (impact + urgency) - 1));
+    target.priority = String(p);
+    log.info('Priority set on insert to ' + p);
+  } catch (e) {
+    log.error('Insert-only priority failed: ' + e.message);
+  }
+})(source, map, log, target);