Use modern mode

[filipsobol]

Short Description and Why It's Useful

This PR enables "modern mode" to CT nuxt build. Everything seems to work flawlessly, but the size of home page is reduced by about 50kB. Boilerplate already uses this mode, so it doesn't require any changes.

Closes #5180.

Which Environment This Relates To

• Test version (https://test.storefrontcloud.io) - this is a new feature or improvement for Vue Storefront. I've created branch from develop branch and want to merge it back to develop
• RC version (https://next.storefrontcloud.io) - this is a stabilisation fix for Release Candidate of Vue Storefront. I've created branch from release branch and want to merge it back to release
• Stable version (https://demo.storefrontcloud.io) - this is an important fix for current stable version. I've created branch from hotfix or master branch and want to merge it back to hotfix

Upgrade Notes and Changelog

• No upgrade steps required (100% backward compatibility and no breaking changes)
• I've updated the Upgrade notes and Changelog on how to port existing Vue Storefront sites with this new feature

┆Issue is synchronized with this Jira Story by Unito

[github-actions]

💙 vsf-next-demo successfully deployed at https://6ae30343999971b6304e91699d17b10f45ec1b92.vsf-next-demo.preview.storefrontcloud.io

[filrak]

@aureate-labs-team keep an eye on it please ;)

[aureate-labs-team]

@filrak Sure 👍