Add GHA release process to push images on tag

.github/workflows/release.yaml

@@ -0,0 +1,55 @@
+name: Cass Operator Release
+
+on:
+  push:
+    tags:
+      - 'v*.*.*'
+  workflow_dispatch:
+    # Allow to rerun this for a tag to get updated UBI-images
+
+jobs:
+  release_cass_operator:
+    name: Release Docker Image
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out code into the Go module directory
+        uses: actions/checkout@v3
+      - name: Set up Go
+        uses: actions/setup-go@v3
+        with:
+          go-version-file: 'go.mod'
+          cache: true
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v2
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v2
+      - name: Login to DockerHub
+        uses: docker/login-action@v2
+        with:
+          username: ${{ secrets.DOCKER_HUB_USERNAME }}
+          password: ${{ secrets.DOCKER_HUB_PASSWORD }}
+      - name: Login to GitHub Container Registry
+        if: ${{ !env.ACT }}
+        uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Set git parsed values
+        id: vars
+        shell: bash
+        run: |
+          echo "sha_short=$(git rev-parse --short=8 ${{ github.sha }})" >> $GITHUB_OUTPUT
+          echo "tag_name=${GITHUB_REF#refs/tags/}" >> $GITHUB_OUTPUT
+          echo "TARGET_VERSION=$(echo ${GITHUB_REF#refs/tags/} | awk '{print substr($0,2)}')" >> $GITHUB_ENV
+      - name: Build and push
+        id: docker_build
+        uses: docker/build-push-action@v3
+        with:
+          load: false
+          file: cmd/kubectl-k8ssandra/Dockerfile
+          push: true
+          tags: k8ssandra/k8ssandra-client:${{ steps.vars.outputs.tag_name }}, ghcr.io/k8ssandra/k8ssandra-client:${{ steps.vars.outputs.tag_name }}
+          platforms: linux/amd64,linux/arm64
+          cache-from: type=local,src=/tmp/.buildx-cache
+          cache-to: type=local,dest=/tmp/.buildx-cache