Externalise backport action

The back porting logic is integrated into each action, duplicated [many times across the codebase](https://github.com/search?q=org%3Ahazelcast+%22Checkout+maintenance+branch+and+cherry-pick%22&type=code).

In hazelcast/hz-docs#1373 this was centralised.

- updated actions to use it
- simplified actions
- updated the list of supported maintenance branches
   - *note* this was very outdated

.github/workflows/backport.yml

@@ -1,40 +1,36 @@
-name: Backport changes to maintenance branches
+name: Backport changes to all maintenance branches
 on:
  push:
   branches:
    - main
 jobs:
-  backport:
-    strategy:
-      matrix:
-        branch: ['v/5.8', 'v/5.9', 'v/5.10']
+  get-maintenance-branches:
     runs-on: ubuntu-latest
+    outputs:
+      branches: "['5.8', '5.9', '5.10', '5.11', '5.12', '5.13', '5.14']"
     steps:
-
-      - name: checkout
-        uses: actions/checkout@v4
-        with:
-         fetch-depth: 0
+      - run: exit 0
 
-      - name: Set up git config
-        run: |
-          git config user.name "GitHub Actions Bot"
-          git config user.email "<>"
-          
-      - name: Check PR for backport label
-        id: check_pr_labels
-        uses: shioyang/[email protected]
-        with:
-         github-token: ${{ secrets.GITHUB_TOKEN }}
-         labels: '["backport"]'
-
-      - name: See result
-        run: echo "${{ steps.check_pr_labels.outputs.result }}"
+  backport-to-all-branch:
+    needs: get-maintenance-branches
+    strategy:
+      fail-fast: true
+      matrix:
+        branch: ${{ fromJSON(needs.get-maintenance-branches.outputs.branches) }}
+    uses: hazelcast/hz-docs/.github/workflows/backport-workflow.yml@main
+    with:
+      label: '["backport to all versions"]'
+      target-branch: v/${{ matrix.branch }}
+    secrets: inherit
 
-      - name: Checkout maintenance branch and cherry-pick
-        if: ${{ steps.check_pr_labels.outputs.result == 'true' }}
-        run: |
-          git fetch
-          git checkout ${{ matrix.branch }}
-          git cherry-pick -x --strategy=recursive -X theirs $GITHUB_SHA
-          git push
+  backport-to-specified-branch:
+    needs: get-maintenance-branches
+    strategy:
+      fail-fast: true
+      matrix:
+        branch: ${{ fromJSON(needs.get-maintenance-branches.outputs.branches) }}
+    uses: hazelcast/hz-docs/.github/workflows/backport-workflow.yml@main
+    with:
+      label: '["backport to ${{ matrix.branch }}"]'
+      target-branch: v/${{ matrix.branch }}
+    secrets: inherit