[Dockerfile] [KubeRay Dashboard]: Fix Dockerfile warnings (ENV format, CMD JSON args) (#4167)

* [#4166] improvement: Fix Dockerfile warnings (ENV format, CMD JSON args)

* extract the hostname from CMD

Signed-off-by: Neo Chien <6762509+cchung100m@users.noreply.github.com>

---------

Signed-off-by: Neo Chien <6762509+cchung100m@users.noreply.github.com>
Co-authored-by: cchung100m <cchung100m@users.noreply.github.com>

Author: cchung100m

dashboard/Dockerfile

@@ -45,7 +45,7 @@ RUN \
 FROM base AS runner
 WORKDIR /app
 
-ENV NODE_ENV production
+ENV NODE_ENV=production
 # Uncomment the following line in case you want to disable telemetry during runtime.
 # ENV NEXT_TELEMETRY_DISABLED 1
 
@@ -67,8 +67,9 @@ USER nextjs
 
 EXPOSE 3000
 
-ENV PORT 3000
+ENV PORT=3000
 
 # server.js is created by next build from the standalone output
 # https://nextjs.org/docs/pages/api-reference/next-config-js/output
-CMD HOSTNAME="0.0.0.0" node server.js
+ENV HOSTNAME="0.0.0.0"
+CMD ["node", "server.js"]