Add docker dir to build mempool containers

docker/backend/Dockerfile

@@ -0,0 +1,28 @@
+FROM node:12-buster-slim AS builder
+
+WORKDIR /build
+COPY . .
+RUN apt-get update
+RUN apt-get install -y build-essential python3 pkg-config
+RUN npm ci --production
+RUN npm i typescript
+RUN npm run build
+
+FROM node:12-buster-slim
+
+WORKDIR /backend
+
+RUN mkdir cache
+
+COPY --from=builder /build/ .
+
+RUN chmod +x /backend/start.sh
+RUN chmod +x /backend/wait-for-it.sh
+
+RUN chown -R 1000:1000 /backend && chmod -R 755 /backend
+
+USER 1000
+
+EXPOSE 8999
+
+CMD ["/backend/start.sh"]