build(Webpack): upgrade webpack to v5

[carlobernardini]

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. Use imperative, present tense in your commit description ("change", not "changed" or "changes") without uppercases or period (.) at the end.

Checklist

• The implementation has been manually tested and complies with Textkernel browser support guidelines
• The implementation complies with accessibility standards.
• The component has a displayName defined.
• The component comes with a detailed PropTypes (and defaultProps) definition.
• Component PropTypes are sufficiently described / documented.
• There is a story in Storybook.

[carlobernardini]

@antipin appreciate it if you could take a look this week.

[antipin]

Shall we keep the base (and thus dev) configs un-minimised, and move it to webpack.prod.conf.js?

[carlobernardini]

Yes, makes sense indeed

[carlobernardini]

Ok I just found out that Storybook doesn't run on Webpack 5 so this is back to square one I'm afraid :(

[antipin]

Blocked on #801