[Website] add lazy loading attr to images

[bullet03]

Resolves #24250

• add loading="lazy" attribute to case-study images. It doesn't decrease the speed of loading, slightly increases it. More case-studies and logos are going to be added soon, so they load only when user scrolls to them. This will improve the speed of page loading

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[AlyaBoiko]

Verified, works as expected. Reviewed and tested by QA

[bullet03]

@aromanenko-dev, could you, please help with review of current PR?