Add build workflow.

.github/workflows/build.yaml

@@ -0,0 +1,47 @@
+name: Build
+
+on:
+  pull_request:
+  push:
+    tags:
+      - "*"
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        rhel: [9]
+
+    steps:
+      - name: Define the tag
+        id: tag
+        shell: bash
+        run: |
+          if [ -n "$GITHUB_HEAD_REF" ]; then
+              echo tag=${GITHUB_HEAD_REF} | sed -E 's,/,-,g'
+          else
+              echo "tag=latest"
+          fi >> ${GITHUB_OUTPUT}
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-buildx-action@v3
+        name: Set up Docker Buildx
+
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          push: true
+          tags: ghcr.io/${{ github.repository }}:${{ matrix.rhel }}-${{ steps.tag.outputs.tag }}
+          file: base-${{ matrix.rhel }}/Dockerfile
+          cache-from: type=gha
+          cache-to: type=gha,mode=max