Docker sample

[ljoy913]

Added a Dockerfile in the sample folder to build and run the Crescent sample in a docker container

• All the project dependencies are installed in the docker image.
• The Crescent source for the image is copied from the local directory at build time, so any changes to the source code will be reflected in the resulting docker image.
• Circom is cloned from its repo and is not copied from the local machine.
• When running the container, the Crescent services will start and be available using the default endpoints. The ports can be changed as parameters to the run command.
• The container will mount a folder called crescent-extention to the local directory that contains the client extension files and the mdl sample file.
• The image build can take 30+ minutes to generate and use 35+GB of disk space.
• Once the image is available, the container can be run with the docker run command.
• Updated sample/README.md to add Docker info.
• The Dockerfile itself contains comments to help build and run.

[christianpaquin]

Build tested on Windows and Ubuntu