Fix broken Case Studies page

[visortelle]

No description provided.

[asafm]

How did it break?

[visortelle]

The problem appeared after this change https://github.com/apache/pulsar-site/pull/858/files#diff-f0b43be5610a8cb248163710fe889d314ca103aea58e38abbf1af3321d8608d0R29
but we quickly noticed it and fixed it.

[visortelle]

Array item index numbers were used for React keys. After shuffling and re-render that led to applying wrong attributes to DOM elements https://github.com/apache/pulsar-site/pull/860/files#diff-f0b43be5610a8cb248163710fe889d314ca103aea58e38abbf1af3321d8608d0L213

---

Another issue is that the server-side rendered HTML version differs from the browser-side version. After hitting the page refresh button, shuffling was executed in the browser, but React keys still corresponded to elements from the server-side version.
I didn't dig much and am not an expert in React SSR.