chore(docs): Add mentioning of HOSTNAME env variable for standalone o…

…utput (#52804)

### What?

Update documentation to mention a `HOSTNAME` env variable for `standalone` output

Related to Feature: #44627 

### Why?

Current documentation mentions only `PORT` env, but does not mention `HOSTNAME` added in January

Affected documentation pages:

- https://nextjs.org/docs/app/api-reference/next-config-js/output

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

### How?

- Run examples
- Check documentation

docs/02-app/02-api-reference/05-next-config-js/output.mdx

@@ -41,6 +41,7 @@ Additionally, a minimal `server.js` file is also output which can be used instea
 >
 > - `next.config.js` is read during `next build` and serialized into the `server.js` output file. If the legacy [`serverRuntimeConfig` or `publicRuntimeConfig` options](/docs/app/api-reference/next-config-js/runtime-configuration) are being used, the values will be specific to values at build time.
 > - If your project uses [Image Optimization](/docs/app/building-your-application/optimizing/images) with the default `loader`, you must install `sharp` as a dependency:
+> - If your project needs alternative port or hostname for listening, you can define `PORT` and `HOSTNAME` environment variables, before running `server.js`. For example, `PORT=3000 HOSTNAME=localhost node server.js`.
 
 </AppOnly>
 

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

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

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

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

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

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

examples/with-docker/Dockerfile

@@ -55,5 +55,6 @@ USER nextjs
 EXPOSE 3000
 
 ENV PORT 3000
+ENV HOSTNAME localhost
 
 CMD ["node", "server.js"]