Fixes problems related to tax calculation and price filter in multistore setup

[juho-jaakkola]

Related Issues

closes #4376

Short Description and Why It's Useful

Screenshots of Visual Changes before/after (if There Are Any)

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

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[gibkigonzo]

@juho-jaakkola thanks for this, please update changelog

[juho-jaakkola]

@gibkigonzo I'm not completely sure what to put into the changelog.

Do you think the text in the commit message would be enough?

[juho-jaakkola]

• Marked the properties in core/lib/types.ts as optional
• Updated the CHANGELOG