chore(#72): github action for building and pushing docker image

.github/workflows/docker-build.yml

@@ -0,0 +1,35 @@
+name: CHT interoperability mediator docker build
+
+on:
+  push:
+    branches:
+      - 'main'
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Build timestamp
+        id: timestamp
+        run: echo "BUILD_TIMESTAMP=$(date +%Y%m%d%H%M)" >> $GITHUB_ENV
+
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v2
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v2
+
+      - name: Login to Docker Hub
+        uses: docker/login-action@v2
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Build and push openhim-mediator
+        uses: docker/build-push-action@v4
+        with:
+          push: true
+          tags: medicmobile/openhim-mediator:${{ env.BUILD_TIMESTAMP }}