Require Jenkins 2.346.3 as minimum Jenkins version

[MarkEWaite]

Require Jenkins 2.346.3 or newer

https://www.jenkins.io/doc/developer/plugin-development/choosing-jenkins-baseline/ recommends either 2.332.4 or 2.346.3.

Also removes the java.level property because that is no longer required with the most recent parent pom.

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