update Docker examples to specify HOSTNAME properly (#59756)

### What?

Update docker examples to correctly set HOSTNAME env variable for
standalone output

Related to PR:
https://github.com/vercel/next.js/pull/52804

### Why?
### TL;DR

The dockerfiile examples need to modified as that contains HOSTNAME
setting that apparently is not working as expected.

Related to Issue:
https://github.com/vercel/next.js/issues/58657

Affected examples:
https://github.com/vercel/next.js/tree/canary/examples/with-docker

https://github.com/vercel/next.js/tree/canary/examples/with-docker-multi-env

### Longer explanations

Based on [Docker
document](https://docs.docker.com/engine/reference/builder/#environment-replacement):
> You can also use environment variables with RUN, CMD, and ENTRYPOINT
instructions, but in those cases the variable substitution is handled by
the command shell, not the builder.

It means that when executing the last CMD ( `node server.js` ) in
Dockerfile samples, the HOSTNAME defined by prior `ENV` instruction is
simply ignored.

This causes problems typically when the host process sets HOSTNAME -
e.g. for instance when using AWS Fargate for deployment [we can't have
control over HOSTNAME](https://stackoverflow.com/a/52871552) set by the
host process. (also refer to the issue #58657 above)

### How?

Updated Dockerfilie samples, by setting HOSTNAME directly in CMD
instruction that launches nextjs server, not in the builder process.

Used this setting at my end (with AWS Fargate) to confirm that it fixes
the network problem.

Closes NEXT-
Fixes #58657

Co-authored-by: Sam Ko <sam@vercel.com>

examples/with-docker-multi-env/docker/development/Dockerfile

@@ -47,6 +47,5 @@ USER nextjs
 EXPOSE 3000
 
 ENV PORT 3000
-ENV HOSTNAME localhost
 
-CMD ["node", "server.js"]
+CMD HOSTNAME=localhost node server.js

examples/with-docker-multi-env/docker/production/Dockerfile

@@ -48,6 +48,5 @@ USER nextjs
 EXPOSE 3000
 
 ENV PORT 3000
-ENV HOSTNAME localhost
 
-CMD ["node", "server.js"]
+CMD HOSTNAME=localhost node server.js

examples/with-docker-multi-env/docker/staging/Dockerfile

@@ -48,6 +48,5 @@ USER nextjs
 EXPOSE 3000
 
 ENV PORT 3000
-ENV HOSTNAME localhost
 
-CMD ["node", "server.js"]
+CMD HOSTNAME=localhost node server.js

examples/with-docker/Dockerfile

@@ -61,9 +61,7 @@ USER nextjs
 EXPOSE 3000
 
 ENV PORT 3000
-# set hostname to localhost
-ENV HOSTNAME "0.0.0.0"
 
 # server.js is created by next build from the standalone output
 # https://nextjs.org/docs/pages/api-reference/next-config-js/output
-CMD ["node", "server.js"]
+CMD HOSTNAME="0.0.0.0" node server.js