Add github actions to build and push operator image (#2)

.github/workflows/ci.yaml

@@ -0,0 +1,10 @@
+on: [push, pull_request]
+name: Test
+jobs:
+  ci:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out the repo
+        uses: actions/checkout@v2
+      - name: Build image
+        run: make operator-image

.github/workflows/publish.yaml

@@ -0,0 +1,26 @@
+name: Publish Docker image
+on:
+  release:
+    types: [published]
+jobs:
+  push_to_registry:
+    name: Push Docker image to GitHub Packages
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out the repo
+        uses: actions/checkout@v2
+      - name: Prepare
+        id: prep
+        run: |
+          DOCKER_IMAGE=ghcr.io/spotify/flink-operator:${GITHUB_SHA::8}
+          echo ::set-output name=image::${DOCKER_IMAGE}
+      - name: Login to Github container registry
+        uses: docker/login-action@v1.1.1
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.CR_PAT }}
+      - name: Push image
+        run: make operator-image push-operator-image
+        env:
+          IMG: ${{ steps.prep.outputs.image }}