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

.github/workflows/on-tag.yml

@@ -34,6 +34,9 @@ jobs:
       - name: Checkout project
         uses: actions/checkout@v2
 
+      - name: Init repo for Dockerization
+        run: docker/init.sh "$TAG"
+
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v1
         id: qemu