feat(ci): add github workflows

Author: Alexandre-io

.github/workflows/docker-image.yml

@@ -0,0 +1,31 @@
+name: Docker Image CI
+
+on:
+  push:
+    tags:
+      - '*.*.*'
+
+jobs:
+
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Extract git tag
+      run: echo "RELEASE_VERSION=${GITHUB_REF#refs/*/}" >> $GITHUB_ENV
+
+    - name: Login to Docker Hub
+      uses: docker/login-action@v1
+      with:
+        username: alexandreio
+        password: ${{ secrets.DOCKERHUB_TOKEN }}
+          
+    - name: Build and push
+      id: docker_build
+      uses: docker/build-push-action@v2
+      with:
+        push: true
+        tags: alexandreio/wordpress_exporter:latest,alexandreio/wordpress_exporter:${{ env.RELEASE_VERSION }}