fix(hero): backgroundImage should cover whole elements area on mobile [ES-387]

[FRSgit]

Related issue

https://alokai.atlassian.net/browse/ES-387

Scope of work

current hero implementation is wrong for mobile devices - background image should try to cover whole element, but without changing it's aspect ratio

add description for best image sizes for hero background

Screenshots of visual changes

Hero on mobile before:

after:

Description:

Checklist

• Self code-reviewed
• Changes documented
• Semantic HTML
• SSR-friendly
• Caching friendly
• a11y for WCAG 2.0 AA
• examples created
• blocks created
• cypress tests created

[changeset-bot]

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Latest commit: 4b1d0e7

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[rohrig]

suggested improvement:

The Hero component simplifies the process of creating stunning hero sections for your website. With Hero, you have the flexibility to seamlessly integrate a main image and customize your content to suit your needs. Additionally, Hero offers optimized background images tailored for both mobile and desktop devices. To ensure an optimal blend of performance and visual appeal, we recommend adhering to the following image guidelines:

Desktop Background Images:
Minimum width: 3840px
Aspect ratio: 4:1.5
Example size: 3840px x 1440px

Mobile Background Images:
Minimum width: 768px
Aspect ratio: 3:4
Example size: 768px x 1024px