This achieves a few things:

1. Creates Dockerfile for sync tool, so that it can be invoked from
   Tekton tasks.
2. Makes sync config directory configurable by flag, so that the tool
   can be ran from any directory. This defaults to sync/config (same as
   before).

Symlinks are retainined in the root directory for requirements.txt and
runtime.txt to satisfy Netlify Build requirements:
https://docs.netlify.com/configure-builds/manage-dependencies/#python

Issue: #34