Unification of webpack config in theme

[psmyrek]

Short Description and Why It's Useful

Currently src/themes/<theme name>/webpack.config.js receives webpack config, but it depends on type of build: for development build this config is wrapped inside default key, but for production build this default key is not present. It is not a problem for default theme, where nothing happens in src/themes/default/webpack.config.js, but it is actually a problem for example in vsf-capybara theme, where some adjustments have been introduced in src/themes/capybara/webpack.config.js.

It would be much simpler and cleaner to always provide webpack config in the same way, regardless of build type.

Which Environment This Relates To

Check your case. In case of any doubts please read about Release Cycle

• 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

IMPORTANT NOTICE - Remember to update CHANGELOG.md with description of your change

Contribution and Currently Important Rules Acceptance

• I read and followed contribution rules