[Cases] Update notify user HTML email template to use current year dynamically (#161327)

## Summary

This PR adds current year dynamcially to notify user HTML email template
footer.


![image](0169d58b-d567-4061-bb7d-36326348aa99)

### Checklist

Delete any items that are not applicable to this PR.

- [x] [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

x-pack/plugins/cases/server/services/notifications/templates/assignees/renderer.ts

@@ -79,6 +79,7 @@ export const assigneesTemplateRenderer = async (
         ? `${caseData.attributes.description.slice(0, DESCRIPTION_LIMIT)}...`
         : caseData.attributes.description,
     url: caseUrl,
+    currentYear: new Date().getUTCFullYear(),
   });
 
   return template;

x-pack/plugins/cases/server/services/notifications/templates/assignees/template.html

@@ -186,7 +186,7 @@
                                 <tr>
                                     <td
                                         style="border-collapse: collapse; mso-table-lspace: 0pt; mso-table-rspace: 0pt; line-height: 24px;">
-                                        © 2022 Elasticsearch B.V. All Rights Reserved.<br />
+                                        © {{currentYear}} Elasticsearch B.V. All Rights Reserved.<br />
                                         Elasticsearch is a trademark of Elasticsearch BV, registered in the
                                         U.S. and in other countries / <a href="https://www.elastic.co/legal/trademarks"
                                             style="text-decoration: none; color: #0071C2; border-width: 0;">Trademarks</a>

x-pack/plugins/cases/server/services/notifications/templates/assignees/template.test.ts

@@ -73,4 +73,13 @@ describe('Assignees template', () => {
 
     expect(container.querySelector('.btn')).not.toBeTruthy();
   });
+
+  it('renders current year correctly', async () => {
+    const currentYear = new Date().getUTCFullYear();
+    const footerText = `© ${currentYear} Elasticsearch B.V. All Rights Reserved.`;
+
+    const container = await getHTMLNode(caseSO, mockCaseUrl);
+
+    expect(getByText(container, footerText, { exact: false })).toBeTruthy();
+  });
 });