Added more example in the to Foreign Keys documentation

[shailpujan88]

This PR is For Add new getting started example https://github.com/vitessio/website/issues/1798

This PR :

1. Added Example to the documentation, illustrating a schema with cyclic dependencies created by cascading foreign key actions.

2. Included a graph depicting the relationships between tables t1, t2, and t3, highlighting the effects of ON DELETE CASCADE and ON UPDATE CASCADE on the schema structure.

3. Specified how to fix the problem caused by the cyclic dependencies

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[deepthi]

oops, didn't realize this is still draft. Reviewers, you may ignore until it is Ready for review.

[deepthi]

@shailpujan88 do you intend to complete this PR? It's still in Draft.