fix(docker): correct healthcheck endpoint in Dockerfile

Fixes the Dockerfile referring to an old healthcheck endpoint. The new
one is under `/ar-io` to avoid potential conflicts with Arweave node
paths.

Dockerfile

@@ -26,7 +26,7 @@ VOLUME /app/data
 
 # EXPOSE PORT AND SETUP HEALTHCHECK
 EXPOSE 4000
-HEALTHCHECK CMD curl --fail http://localhost:4000/healthcheck || exit 1
+HEALTHCHECK CMD curl --fail http://localhost:4000/ar-io/healthcheck || exit 1
 
 # ADD LABELS
 LABEL org.opencontainers.image.title="ar.io Core Service"