[mock-chronik-client] Configure for automated npm publishing

Summary: Initialize Docker file(s) for build step of automated npm publishing

Test Plan:

docker build -t mock-chronik-client_local .
docker run --rm --name mock-chronik-client mock-chronik-client_local

receive expected auth error as we don't have the token locally

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D15653