Upgrade Webpack to v5, switch to Node v18

[ljowen]

In order to support COGs we need to use node v18.
Breaking changes with node v17 and Webpack v4 necessitate updating webpack to v5: see webpack/webpack#14532

[nf-s]

No longer needed for COG work - so lower priority

[pjonsson]

Breaking changes with node v17 and Webpack v4 necessitate updating webpack to v5: see webpack/webpack#14532

I think that issue is avoided with https://github.com/webpack/webpack/releases/tag/v4.47.0.