Only build ndc-postgres binary in Docker (#213)

<!-- The PR description should answer 2 (maybe 3) important questions:
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### What

Dockerfile is building too much stuff it doesn't need.

### How

Only build the `ndc-postgres` binary.

ConfigServer.Dockerfile

@@ -14,7 +14,7 @@ ENV RUSTFLAGS="-C link-arg=-fuse-ld=lld"
 
 COPY . .
 
-RUN cargo build --release --all-targets
+RUN cargo build --release --bin ndc-postgres
 
 ## Copy the binaries and serve the configuration server
 FROM debian:buster-slim as ndc-postgres