Category Add Products mutation needs to use nonReactiveState

[grimasod]

Related issues

closes #

Short description and why it's useful

The Category Set Products mutation adds full product data to nonReactiveState and saves only the SKU in state.products. When adding more products (for example when onBottomScroll is triggered on a Category page) the Category Add Products mutation must do the same.

Also removed an unnecessary cloneDeep operation - there's no need to deep copy a 1-dimensional array returned my the map function

Screenshots of visual changes before/after (if there are any)

Which environment this relates to

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• 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

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