[CI] update backport custom branch name (opensearch-project#2766)

GitHub action for backporting got updated to change custom branch
to head template.

This was causing issues in clean up and skipping steps.

Issue:
n/a

Signed-off-by: Kawika Avilla <kavilla414@gmail.com>
Signed-off-by: David Sinclair <david@sinclair.tech>

.github/workflows/backport.yml

@@ -37,5 +37,5 @@ jobs:
         uses: VachaShah/backport@v2.1.0
         with:
           github_token: ${{ steps.github_app_token.outputs.token }}
-          branch_name: backport/backport-${{ github.event.number }}
+          head_template: backport/backport-<%= number %>-to-<%= base %>
           files_to_skip: "CHANGELOG.md"

CHANGELOG.md

@@ -59,6 +59,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ### 🚞 Infrastructure
 
 - Add CHANGELOG.md and related workflows ([#2414](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/2414))
+- Update backport custom branch name to utilize head template ([#2766](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/2766))
 
 ### 📝 Documentation