Re-implement Docker workflow using GitHub Actions (#326)

* Recreate a docker dir with all docker files inside and add init.sh
* Add docker/README.md with example docker-compose.xml
* Add mysql vars for mempool-config.json
* Port can be set from env var in docker-compose.xml
* Update docker-compose.xml example to use latest tag
* Remove armv7 architecture from build workflow
* Remove master git-hash file
* Remove useless ':' in sed

docker/frontend/Dockerfile

@@ -0,0 +1,34 @@
+FROM node:12-buster-slim AS builder
+
+WORKDIR /build
+COPY . .
+RUN apt-get update
+RUN apt-get install -y build-essential rsync
+RUN npm i
+RUN npm run build
+
+FROM nginx:1.17.8-alpine
+
+WORKDIR /patch
+
+COPY --from=builder /build/entrypoint.sh .
+COPY --from=builder /build/wait-for .
+COPY --from=builder /build/dist/mempool /var/www/mempool
+COPY --from=builder /build/nginx.conf /etc/nginx/
+COPY --from=builder /build/nginx-mempool.conf /etc/nginx/conf.d/
+
+RUN chmod +x /patch/entrypoint.sh
+RUN chmod +x /patch/wait-for
+
+RUN chown -R 1000:1000 /patch && chmod -R 755 /patch && \
+        chown -R 1000:1000 /var/cache/nginx && \
+        chown -R 1000:1000 /var/log/nginx && \
+        chown -R 1000:1000 /etc/nginx/nginx.conf && \
+        chown -R 1000:1000 /etc/nginx/conf.d
+RUN touch /var/run/nginx.pid && \
+        chown -R 1000:1000 /var/run/nginx.pid
+
+USER 1000
+
+ENTRYPOINT ["/patch/entrypoint.sh"]
+CMD ["nginx", "-g", "daemon off;"]