chore(docker): copy web assets from the build image

Signed-off-by: Mark Sagi-Kazar <mark.sagikazar@gmail.com>

Dockerfile

@@ -46,7 +46,7 @@ USER 1001:1001
 
 # Import frontend assets and set the correct CWD directory so the assets
 # are in the default path.
-COPY web web
+COPY --from=builder /usr/local/src/dex/web web
 
 ENTRYPOINT ["dex"]