feat(vue-demo-store): a11y improvements

[mkucmus]

Description

closes: #401

solves all critical and serious issues. Some contrast issues cannot be tracked and found to fix (hidden DOM elements 🤔 probably). there are still some small issues in "alert" level mainly for redundant links for product (described in notes section).

In order to fix many of contrast errors, I needed to tweak up the level of text colors, like for:
text-blue-500 -> text-blue-600, and so on. would be good to see if it goes aligned to our visual identity (if there is any).

Notes

• dynamic content coming from API (CMS) cannot be fixed in the project. keep in mind that HTML from Shopping Experiences is not always valid in terms of accessibility rules.
• there is a problem with redundant links (see link purposes guideliness) with Product card -> one link for product's title, second for product image. we can rethink the structure of Product Card in order to place add to wishlist links in outer area to make possible wrapping in a link the image and title together.

Used tools

• https://github.com/vue-a11y/vue-axe
• Wave evaluation tool (chrome extension)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Screenshots (if applicable)

Additional context

[vercel]

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Name	Status	Preview	Updated (UTC)
frontends-demo	✅ Ready (Inspect)	Visit Preview	Oct 2, 2023 7:18am
shopware-frontends-docs	✅ Ready (Inspect)	Visit Preview	Oct 2, 2023 7:18am