Added a build workflow.

Author: rudimk

.github/workflows/build.yml

@@ -0,0 +1,42 @@
+name: build
+
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  build:
+    runs-on: ubicloud-standard-8
+    environment: production
+    steps:
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Login to GitHub Package Registry
+        uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Checkout the postgres-extensions repo
+        uses: actions/checkout@v4
+        with:
+          submodules: true
+          fetch-depth: 0
+          token: ${{ secrets.GITHUB_TOKEN }}
+      - name: Get tag
+        id: tagger
+        run: echo "::set-output name=tag::$(git describe --tags HEAD)"
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        env:
+          DOCKER_BUILDKIT: 1
+        with:
+          context: .
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: |
+            ghcr.io/porter-dev/postgres-extensions:${{ steps.tagger.outputs.tag }}
+            ghcr.io/porter-dev/postgres-extensions:latest