[JENKINS-73253] Build and test with Java 21

[MarkEWaite]

Build and test with Java 21

Jenkins will require Java 17 or newer in weekly releases beginning June 18, 2024. Jenkins has supported Java 21 for a long time. I've been using Java 21 for my local development work without any issue.

The upgrade to Spring Framework 6 will require at least Java 17. Let's move to Java 21 to prepare for the future.

JENKINS-67909 is the Jira epic that tracks the Java 11 end of life. JENKINS-73253 is the issue for this pull request

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1. Check that the `$pluginId Developers` team has `Admin` permissions while granting the access.

   Check that the $pluginId Developers team has Admin permissions while granting the access.
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2. In the case of plugin adoption, ensure that the Jenkins Jira default assignee is either removed or changed to the new maintainer.

   In the case of plugin adoption, ensure that the Jenkins Jira default assignee is either removed or changed to the new maintainer.
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3. If security contacts are changed (this includes add/remove), ping the security officer (currently `@Wadeck`) in this pull request. If an email contact is changed, wait for approval from the security officer.

   If security contacts are changed (this includes add/remove), ping the security officer (currently @Wadeck) in this pull request. If an email contact is changed, wait for approval from the security officer.
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[dduportal]

For info, this PR broke the deployment in trusted.ci as there are no maven-21 agent template (yet).

Opened jenkins-infra/helpdesk#4122 to track this.