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

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh ./bin/configs/*.yaml
  ./bin/utils/export_docs_generators.sh
  

• File the PR against the correct branch: master (upcoming 7.x.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

@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.