[cpp-pistache-server] Adds Recursive model validation

[ventsyv]

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Proposed solution for: #15781
Detailed explanation of the issue is in the ticket.

@ravinikam @stkrwork @etherealjoy @MartinDelille @muttleyxd

[wing328]

Thanks for the PR but your commit (as shown in the Commits tab) is not linked to your Github account, which means this PR won't count as your contribution in https://github.com/OpenAPITools/openapi-generator/graphs/contributors.

Let me know if you need help fixing it.

Ref: https://github.com/OpenAPITools/openapi-generator/wiki/FAQ#how-can-i-update-commits-that-are-not-linked-to-my-github-account

[ventsyv]

@wing328 Good catch. I updated it.

[wing328]

If no further feedback/question, I'll merge it later this week.