Update Boilerplate to work with unified composables

[filipsobol]

Short Description and Why It's Useful

Update Boilerplate to work with new, unified composables. More details can be found here: #5299

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

[coveralls]

Pull Request Test Coverage Report for Build 438425533

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.241%

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Totals
Change from base Build 436132113:	0.0%
Covered Lines:	1353
Relevant Lines:	1419

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💛 - Coveralls

[github-actions]

💙 vsf-next-demo successfully deployed at https://e71688fd58dd0b710197aa97a988f9a5a95da777.vsf-next-demo.preview.storefrontcloud.io