WIP: Add script to build Docker alpine container from project root directory

[ltfschoen]

Adds a shell script for running a detached Docker container of Alpine Linux from openethereum's root directory (similar to that provided for Centos). It shows how the user may then use docker exec -it eth1.0-openethereum ./openethereum --version to connect to a bash session in the container to run a openethereum commands.

This is a WIP since I'm still testing it out myself since I need to run a separate Eth1.0 node for my Eth2.0 validator node to sync with in this example ethereum/staking-deposit-cli#83

Currently it returns error

The command '/bin/sh -c cargo build --release --features final --target x86_64-alpine-linux-musl --verbose' returned a non-zero code: 101
Running OpenEthereum:
Unable to find image 'eth1.0:openethereum' locally
docker: Error response from daemon: pull access denied for eth1.0, repository does not exist or may require 'docker login': denied: requested access to the resource is denied.
See 'docker run --help'.
Echoing OpenEthereum version:
Error: No such container: eth1.0-openethereum
Done.