multi stage Dockerfile and Taskfile

[mscurtescu]

• switching to a multi stage Dockerfile
  • build stage has golang
  • installs the node binary
  • installs the grpcurl tool
  • the target stage based on Alpine Linux
  • copies over the node and grpcurl binaries and a couple of json files
  • much smaller image, 151MB vs 1.18GB
  • safer since neither source code nor go are present in production
• adding Taskfile task runner to help with building and running
• adding healthcheck to docker-compose.yml
• docker-compose.yml can be customised through .env
  • .env.example provided as a sample