ci/cd: build and push zot container images

to github's container registry, closes #188

.github/workflows/publish-docker-image.yml

@@ -0,0 +1,24 @@
+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: Log in to GitHub Docker Registry
+        uses: docker/login-action@v1
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Build container image
+        uses: docker/build-push-action@v2
+        with:
+          push: true
+          tags: |
+            ghcr.io/${{ github.repository }}:latest
+            ghcr.io/${{ github.repository }}:${{ github.event.release.tag_name }}

.travis.yml

@@ -19,6 +19,16 @@ install:
 script:
   - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then travis_wait 60 make; fi
 
+deploy:
+  skip_cleanup: true
+  provider: releases
+  api_key:
+    secure: "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"
+  file_glob: true
+  file: bin/zot*
+  on:
+    tags: true
+
 after_success:
   - bash <(curl -s https://codecov.io/bash)