update default JDK version

[jetersen]

JDK 11 have been required as the default for newer plugins at what time is it good thing to switch this here in the buildPlugin?

It's been 4 almost 5 months since blog post about JDK 11

https://www.jenkins.io/blog/2022/12/14/require-java-11/

[lemeurherve]

See the comments on #514

Doing that would require batch updates of every plugin's Jenkinsfile first for not breaking them with this default value change. (planned)

[MarkEWaite]

As far as I can tell as a first approximation, that change will break 600 of the 1150+ plugins that have a Jenkinsfile. I think it is much better to submit the pull requests to the individual plugins proposing to make their use of Java 8 explicit.

As a different question, is there enough benefit to the Jenkins project to make this change ever? I agree that plugins should be moving to require Jenkins 2.361.4 or newer and should require Java 11, but that is a long process that will take years.

[jglick]

Discussed in #514.

[MarkEWaite]

I'm closing this pull request because we'd rather retain compatibility for existing users and place the changes into the callers. It can be reopened if we find the need in the future.