[JENKINS-71922] Support Java 21

[alecharp]

Related to JENKINS-71922

The usage of Lombok was introduced in 5972f75.
The dependency was used only to remove a few lines of code which can generally be generated by any IDE.

There is no usages of the library outside of the CredentialsListBoxModel class, so it seems a bit overkill to use the library. Removing it to be compatible with Java 21 seems quicker.

Testing done

Ran mvn verify with Java 21, no issue.
Ran mvn hpi:run using Java 21 but faced issue when trying to use the plugin in Google Compute Engine where creating a compute-engine node in Jenkins yields an issue about not finding configure-entries.jelly for ComputeEngineInstance class.

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4. Link to relevant issues in GitHub or Jira
5. Link to relevant pull requests, esp. upstream and downstream changes
6. Ensure you have provided tests - that demonstrates feature works or fixes the issue

[alecharp]

To be useful, the PR should be reopened by a maintainer or an admin so that the Jenkinsfile is used.

[basil]

Replayed the run with Jenkinsfile changes here:

https://ci.jenkins.io/job/Plugins/job/google-oauth-plugin/job/PR-184/3/

Build is green

[alecharp]

@jenkinsci/google-oauth-plugin-developers do you think this could be merged and released?

[jtnord]

https://github.com/jenkinsci/google-oauth-plugin/releases/tag/google-oauth-plugin-1.0.11