Document webpack change: feat: support `node:` prefix for Node.js core modules in runtime code

[webpack-bot]

A pull request by @alexander-akait was merged and maintainers requested a documentation change.

See pull request: https://github.com/webpack/webpack/pull/18316

---

What kind of change does this PR introduce?

fixes https://github.com/webpack/webpack/issues/18277

Did you add tests for your changes?

Yes

Does this PR introduce a breaking change?

No, because we generate it only when your env supported it

What needs to be documented once your changes are merged?

Yes

Shorty:

We generate node: prefix for import ... from "module" only when your env supported it and it is only abour webpack runtime code. We need document that you can disable it using the output.environment.nodePrefixForCoreModules option