[Feature Request]: Support esm exports for config files

[RobinClowers]

What problem does this feature solve?

Typescript and node support esm, and it's confusing that the config file requires using a commonjs export.

What does the proposed API of configuration look like?

Rspack should look for a default export first, and fall back to using the named exports if it doesn't find the default export.

[hardfist]

rspack supports esm config https://github.com/web-infra-dev/rspack/blob/main/packages/rspack-cli/tests/build/basic/entry.config.mjs

[RobinClowers]

Oh cool, I will try that out! Seems like it needs to be added to the docs, unless I missed it?

[hyf0]

Closed for having web-infra-dev/rspack-website#267.