feat (#19407 JAVA SPRING WEBCLIENT): Add support for useSingleRequestParameter to Spring WebClient

[Nicklas2751]

As Requested with #19407 I added support for useSingleRequestParameter to the Spring WebClient

Closes #19407

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  ./mvnw clean package 
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@bbdouglas (2017/07) @sreeshas (2017/08) @jfiala (2017/08) @lukoyanov (2017/09) @cbornet (2017/09) @jeff9finger (2018/01) @karismann (2019/03) @Zomzog (2019/04) @lwlee2608 (2019/10) @martin-mfg (2023/08)

[Nicklas2751]

1 check failed because I rebased my branch with the current master branch which triggered the (not working) scala action

[wing328]

https://github.com/OpenAPITools/openapi-generator/actions/runs/11280772589/job/31374692898?pr=19827

please update the samples when you've time

[Nicklas2751]

@wing328 This is done. I also rebased with the latest upstream master :)

[wing328]

Sorry for the delay. Just merged the PR.

Thanks again for your contribution.