fix(Dockerfile): Navigate Docker's wonky COPY command.

[jtk54]

I tested this locally on a Docker container and verified that
the config directory structure looks how we actually want it to this
time. @duftler FYI. Sorry for the repeated attempts to solve this.

[jtk54]

COPY <from> <to>

Apparently when to is a directory that doesn't exist yet on a container, COPY makes a directory when from is a directory. When to does exist, COPY copies the files in from into to and doesn't actually create a from directory in to. That's a least my understanding of the way this thing behaves. Not consistent with linux cp.