Write a tink-worker-init binary that set the stage for the tink worker to run

[gianarb]

Hey!

as we spoke recently and looking at #2 you figured out how to reliably interact with docker.sock from inside a service.

The box has to be provisioned with:

1. A tink-worker configuration file in YAML format that can be passed to the tink-worker container
2. It has to download and place registry TLS certificate in the right directory

We ended up with the idea of building a binary that will run before the docker-init script in LinuxKit and will setup those bits.

[gianarb]

@thebsdbox solved it easily #5