chore(cicd): New workflow to create/update main branch with master ch…

…anges (#29867)

Refs: #29840 

### Proposed Changes
* Branch `main` is created if not exists
* `main` is updated each time a PR gets merged into master

---------

Co-authored-by: Daniel Enrique Colina Rodríguez <[email protected]>

.github/workflows/cicd_post_sync-main-with-master.yml

@@ -0,0 +1,39 @@
+## Temp workflow to keep the main branch synchronized with changes in master.
+## This workflow will be deleted after finishing the migration from master to main.
+## Epic: https://github.com/dotCMS/core/issues/29554
+name: Sync main with master
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  sync-main:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: 'Setup git config'
+        run: |
+          git config user.name "${{ secrets.CI_MACHINE_USER }}"
+          git config user.email "[email protected]"
+          
+      - name: Checkout code
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0 # Fetch all history for all branches
+
+      - name: Create or update main branch
+        run: |
+          # Check if 'main' branch exists
+          if git show-ref --quiet refs/heads/main; then
+            # If 'main' branch exists, update it to match 'master'
+            git checkout main
+            git reset --hard origin/master
+          else
+            # If 'main' branch does not exist, create it from 'master'
+            git checkout -b main origin/master
+          fi
+
+          # Push the updated main branch
+          git push origin main --force