chore(ci): publish the staging Docker image with goreleaser (#179)

Publish the staging Docker image (ghcr.io/italia/developers-italia-api:main)
when pushing to main.

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

@@ -0,0 +1,41 @@
+# Push the staging Docker image (ghcr.italia/developers-italia-api:main)
+# on updates to main.
+
+on:
+  push:
+    branches: [ main ]
+
+permissions:
+  # To push Docker images to GitHub
+  packages: write
+
+jobs:
+  goreleaser:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        uses: actions/setup-go@v3
+        with:
+          go-version: 1.18.x
+      -
+        uses: actions/checkout@v2
+        with:
+          # All history, required for goreleaser
+          fetch-depth: 0
+      -
+        # FIXME: goreleaser should already take care of the login
+        # (see https://github.com/goreleaser/goreleaser/blame/02a3486d4ba59505113a57b438ae567351ed3dab/scripts/entrypoint.sh#L17)
+        # but it doesn't work for some reason.
+        run: echo "$GITHUB_TOKEN" | docker login ghcr.io -u docker --password-stdin
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+      -
+        # Tag with a temporary valid semantic version. This is required by goreleaser.
+        run: git tag $(git describe --tags --abbrev=0)-main-$(git rev-parse --short HEAD)
+
+      -
+        uses: goreleaser/goreleaser-action@v2
+        with:
+          version: v1.9.2
+          args: release --config .goreleaser.staging.yaml

.goreleaser.staging.yaml

@@ -0,0 +1,21 @@
+# Goreleases configuration for staging builds, just builds and pushes
+# the Docker image for the main branch.
+#
+# Make sure to check the documentation at https://goreleaser.com
+
+# Don't create a GitHub release
+release:
+  disable: true
+
+builds:
+  - env:
+      - CGO_ENABLED=0
+    ldflags:
+     - -s -w
+    goos:
+      - linux
+dockers:
+ -
+   dockerfile: Dockerfile.goreleaser
+   image_templates:
+     - "ghcr.io/italia/developers-italia-api:main"

Dockerfile

@@ -1,6 +1,6 @@
 #
 # This is for local development only.
-# See Dockerfile.goreleaser for the image published on release.
+# See Dockerfile.goreleaser for the image published on release or staging.
 #
 
 FROM golang:1.18 as base