added post release workflow

Author: Rishab87

.github/workflows/post-release.yml

@@ -0,0 +1,99 @@
+name: Post Release
+on:
+  workflow_dispatch:
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  promote-image:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Extract Go version
+        id: version
+        run: |
+          # Extract Go version from Dockerfile
+          GO_VERSION=$(grep '^ARG GOVERSION=' Dockerfile | cut -d'=' -f2)
+          echo "go-version=${GO_VERSION}" >> $GITHUB_OUTPUT
+        
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: ${{ steps.version.outputs.go-version }}
+          
+      - name: Install kpromo
+        run: go install sigs.k8s.io/promo-tools/v4/cmd/kpromo@latest
+        
+      - name: Get latest pre-release tag
+        id: extract_tag
+        run: |
+          TAG=$(gh release list --limit 1 --json tagName,isPrerelease --jq '.[] | select(.isPrerelease == true) | .tagName')
+          if [ -z "$TAG" ]; then
+            echo "Error: No pre-release found"
+            exit 1
+          fi
+          echo "tag=${TAG}" >> $GITHUB_OUTPUT
+          echo "Found pre-release tag: ${TAG}"
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        
+      - name: Create image promotion PR
+        run: |
+          kpromo pr --fork=${{ github.actor }} --interactive=false \
+            --project=kube-state-metrics \
+            --tag=${{ steps.extract_tag.outputs.tag }}
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+  merge-back-to-main:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          
+      - name: Get latest pre-release tag
+        id: extract_tag
+        run: |
+          TAG=$(gh release list --limit 1 --json tagName,isPrerelease --jq '.[] | select(.isPrerelease == true) | .tagName')
+          if [ -z "$TAG" ]; then
+            echo "Error: No pre-release found"
+            exit 1
+          fi
+          echo "tag=${TAG}" >> $GITHUB_OUTPUT
+          echo "Found pre-release tag: ${TAG}"
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        
+      - name: Create PR to merge release changes back to main
+        run: |
+          # Extract major.minor for branch name
+          MAJOR_MINOR=$(echo "${{ steps.extract_tag.outputs.tag }}" | sed 's/v//' | cut -d. -f1,2)
+          RELEASE_BRANCH="release-${MAJOR_MINOR}"
+          
+          # Check if branches exist and have differences
+          if ! git rev-parse --verify "origin/${RELEASE_BRANCH}" >/dev/null 2>&1; then
+            echo "Error: Branch ${RELEASE_BRANCH} does not exist"
+            exit 1
+          fi
+          
+          # Check if there are commits to merge
+          if git merge-base --is-ancestor "origin/${RELEASE_BRANCH}" origin/main; then
+            echo "No commits to merge - ${RELEASE_BRANCH} is already merged into main"
+            exit 0
+          fi
+          
+          gh pr create \
+            --title "chore: Merge ${{ steps.extract_tag.outputs.tag }} back to main" \
+            --body "Merge release changes from ${{ steps.extract_tag.outputs.tag }} back to main branch." \
+            --base main \
+            --head $RELEASE_BRANCH \
+            --reviewer @sig-instrumentation-approvers \
+            --assignee @sig-instrumentation-leads
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}