Support for trailing slash

[Fifciu]

Related Issues

closes #4684

Short Description and Why It's Useful

PR based on #4716
It adds support for the trailing slash. Routes will work both with and without trailing slash. We didn't want to force anything on each route because some projects might require trailing slash for a PLP but not for a PDP. If you want to apply redirects, we are going to prepare a simple doc about that: https://github.com/vuestorefront/vue-storefront/issues/5370

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

[CLAassistant]

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