Require Jenkins 2.479.3 and Jakarta EE 9

[strangelookingnerd]

Require Jenkins 2.479.3 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]

@stuartrowe Kindly requesting a review.

[stuartrowe]

@strangelookingnerd I'm not a maintainer of this plugin so I don't think I'm qualified to review it.

@skumar7322 would be the best to review it.

[skumar7322]

Hi @strangelookingnerd thanks for creating this PR.
There are too many files in this PR. If possible could you please break this in multiple PRs(max 30 files per commit).
The decision to update Jenkins version is taken by us, after analysing the number of impacted users. Remove Jenkins version and java version changes.
Really appreciate you efforts for these changes.

[strangelookingnerd]

9a7e8e8 contains the most important changes that are more or less required.

b60493d contains changes that are optional to a certain extent, however I'd highly recommend considering them to improve code quality and maintainability. I don't see the point of breaking that up into smaller commits.

[skumar7322]

I will run our test suite for this PR.