[REQ] Upgrade ktor to 3.4.0

[luisvt]

• Upgrade ktor to 3.4.0
• Upgrade kotlin to 2.3.0

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 || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in WSL)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• 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 solves a reported issue, reference it using GitHub's linking syntax (e.g., having "fixes #123" present in the PR description)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

@karismann @Zomzog @andrewemery @4brunu @yutaka0m @stefankoppier @e5l @dennisameling

---

Summary by cubic

Upgraded Kotlin server templates and samples to Ktor 3.4.0 and Kotlin 2.3.0, switching to the io.ktor Gradle plugin, removing the Ktor BOM, and updating build scripts (e.g., mainClass assignment).

• Dependencies

  • Ktor 3.4.0 + io.ktor.plugin 3.4.0
  • Kotlin 2.3.0
  • Gradle wrapper 9.2.1

• Migration

  • Regenerate Kotlin server projects to pick up new versions.
  • For existing projects, apply io.ktor.plugin, remove the Ktor BOM and the standalone application plugin, set application.mainClass as a string, and use Gradle ≥ 9.2.1.

^{Written for commit 688dfac. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 9 files

[wing328]

Upgrade gralde-wrapper to 9.2.1

thanks for the PR. can you please separate that into another PR given that gradle 8.x is still supported?

[luisvt]

Sure, I'll do it

[luisvt]

@wing328 I just removed the change for upgrading gradle

[wing328]

please update

openapi-generator/.github/workflows/samples-kotlin-server-jdk17.yaml

Line 30 in 8836013

GRADLE_VERSION: '8.10'

to newer version to address the build failure

[luisvt]

I just rebased to latest from master and force pushed

[wing328]

merged via #23164 with minor changes in the workflow files