Require Jenkins 2.479.3 or newer and Jakarta EE 9

[strangelookingnerd]

Require Jenkins 2.479.3 or newer and Jakarta EE 9

Jenkins 2.479.3 provides Jakarta EE 9, Eclipse Jetty 12, Spring Security 6, and Java 17.

• Update plugin pom and baseline
• Remove deprecations
• Use Java 17 language features
• Minor cleanup

Testing done

mvn clean verify

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[strangelookingnerd]

Build fails due to the Java 17 requirement that comes with Jenkins 2.479.3. The Jenkinsfile has been updated however it is not considered by ci.jenkins.io for building this PR.

I recommend verifying these changes manually.

[strangelookingnerd]

@zaman-akib Kindly requesting a review.

[zaman-akib]

@strangelookingnerd Thanks for the suggestion to upgrade the Jenkins version. While we are planning to raise the minimum supported version soon, we currently have a few customer dependencies that are still on older Jenkins versions. To maintain compatibility for those users, we are continuing to use Jenkins 2.440 for now. We'll revisit this upgrade once those dependencies have been addressed.