Httplib server codegen

[rajvesh]

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• Read the contribution guidelines.
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[rajvesh]

Hello @wing328 ,
Previous pull request got closed. I don't know the reason.
(#21672)

This is the same code with rework on your comments from previous.

Thank you.

[wing328]

https://github.com/OpenAPITools/openapi-generator/actions/runs/16865113770/job/47794205903?pr=21724

you can search for toLowerCase in the project and see how other generators call this function to address the build failure