fix: show browser prompt if user close the page with unsaved changes (elastic#235324)

## Before


https://github.com/user-attachments/assets/5a7d4fd4-c185-4c25-a931-38c5d47d0a7d

## After


https://github.com/user-attachments/assets/65f3f9f9-32d8-4bc9-88f4-0e57e2851d81


### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This was checked for breaking HTTP API changes, and any breaking
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`release_note:breaking` label should be applied in these situations.
- [ ] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [ ] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
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- [ ] Review the [backport
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and apply applicable `backport:*` labels.

### Identify risks

Does this PR introduce any risks? For example, consider risks like hard
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Describe the risk, its severity, and mitigation for each identified
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- [ ] [See some risk
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- [ ] ...

Author: Kiryous

src/platform/plugins/shared/workflows_management/public/shared/ui/unsaved_changes_prompt.tsx

@@ -27,6 +27,20 @@ export const UnsavedChangesPrompt: React.FC<Props> = ({
     currentPathRef.current = location.pathname;
   }, [location.pathname]);
 
+  useEffect(() => {
+    const handler = (event: BeforeUnloadEvent) => {
+      if (hasUnsavedChanges) {
+        // These 2 lines of code are the recommendation from MDN for triggering a browser prompt for confirming
+        // whether or not a user wants to leave the current site.
+        event.preventDefault();
+        event.returnValue = '';
+      }
+    };
+    // Adding this handler will prompt users if they are navigating to a new page, outside of the Kibana SPA
+    window.addEventListener('beforeunload', handler);
+    return () => window.removeEventListener('beforeunload', handler);
+  }, [hasUnsavedChanges]);
+
   const message = (nextLocation: any) => {
     const nextPath: string | undefined = nextLocation?.pathname;
     const currentPath = currentPathRef.current;