add case study for yelp streaming

[hspandher]

Publish blog https://engineeringblog.yelp.com/2024/03/building-data-abstractions-with-streaming-at-yelp.html as apache beam case study.

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[aaltay]

Thank you @hspandher !

Here is the staging link: https://apache-beam-website-pull-requests.storage.googleapis.com/33143/case-studies/index.html

This looks great. I will merge it. No need to review, as this is already published on Yelp's own blog.

@liferoad - could you please ask someone to make 2 follow up changes:

1. The width of the content somehow is less than the page width. Probably some html tag is limiting the width. (You can compare to other case studies.)
2. Add a note at the bottom saying that, "This blog was originally published on Yelp's engineering blog on March 2024 at " (link = https://engineeringblog.yelp.com/2024/03/building-data-abstractions-with-streaming-at-yelp.html