Add webpack build to webpack guide

[julien-deramond]

Description

This PR suggests to enhance the Webpack guide with some references to webpack build / npm run build which is mentioned in the last sections.

It also adds some consistency with https://github.com/twbs/examples/tree/main/webpack project and is linked to twbs/examples#28.

Note: I've reintroduced here the comments from https://github.com/twbs/examples/blob/main/webpack/webpack.config.js but maybe we can just drop them in this file and revert my modification with the comments.

Question: Do we need to add a build command for Vite and Parcel as well?

Type of changes

• Enhancement

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• (NA) I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-37796--twbs-bootstrap.netlify.app/docs/5.3/getting-started/webpack/

Related issues

Closes #37793

[mdo]

Thanks!