feat(ci): use ghcr and auto release

- Pushes images to GitHub Container Registry (GHCR) to deprecate Docker Hub
- Auto releases for nightly
- Auto releases for new release

.github/workflows/release.yaml

@@ -0,0 +1,45 @@
+name: Release
+on:
+  push:
+    branches:
+      - master
+jobs:
+  release-please:
+    name: Run release-please
+    runs-on: ubuntu-latest
+    outputs:
+      release_created: ${{ steps.release.outputs.release_created }}
+      tag_name: ${{ steps.release.outputs.tag_name }}
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+      - name: Setup release please
+        uses: google-github-actions/release-please-action@v2
+        id: release
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          release-type: simple
+          changelog-path: CHANGELOG.md
+          package-name: gonic
+  build-tag-publish:
+    name: Build, tag, and publish Docker image
+    if: ${{ needs.release-please.outputs.release_created }}
+    needs: release-please
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+      - name: Update version.go
+        run: sed -Ei 's/VERSION = "v0.0.0"/VERSION = "${{ needs.release-please.outputs.tag_name }}"/g' version/version.go
+      - name: Login into GitHub Container Registry
+        run: echo ${{ secrets.CR_PAT }} | docker login ghcr.io -u $GITHUB_ACTOR --password-stdin
+      - name: Build Docker image
+        if: ${{ needs.release-please.outputs.release_created }}
+        run: |
+          docker build \
+          -t "ghcr.io/${GITHUB_REPOSITORY}:${{ needs.release-please.outputs.tag_name }}" \
+          -t "ghcr.io/${GITHUB_REPOSITORY}:latest" .
+      - name: Release Docker image
+        run: |
+          docker push "ghcr.io/${GITHUB_REPOSITORY}:${{ needs.release-please.outputs.tag_name }}"
+          docker push "ghcr.io/${GITHUB_REPOSITORY}:latest"