Removed chevron arrows when only one product image

[RGijsberts]

Related issues

closes #2911

Short description and why it's useful

Issue #2911 stated that when there is only 1 product image the gallery navigation still shows even though you can't scroll. The same goes for then you reach the end of the gallery and can't scroll any further to the left or right; it would still show a navigation arrow for that direction (but in 0.3 opacity.

My fix hides the navigation arrow on class '.VueCarousel-navigation--disabled'.

The result; when there is only 1 product image OR when you can't scroll further towards a direction, it will hide the navigation arrow.

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

Before

After

Obviously on products with only 1 image both navigation arrows will be hidden.

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 VS sites with this new feature

Contribution and currently important rules acceptance

• I read and followed contribution rules
• I read the TypeScript Action Plan and adjusted my PR according to it
• I read about Vue Storefront Modules and I am aware that every new feature should be a module