Update to latest parent pom jenkins:1.51

[batmat]

No JIRA.
Picks up the three following PRs:

• Update to extra-enforcer-rules with JDK 11 support pom#36
• Update plugins pom#37
• [JENKINS-55162] - Update to Maven JAR Plugin 3.1.1 to pick up the fix of MJAR-241 pom#38

Proposed changelog entries

• Update to parent pom jenkins:1.51. Changelog.

Submitter checklist

• JIRA issue is well described
• Changelog entry appropriate for the audience affected by the change (users or developer, depending on the change). Examples
  * Use the Internal: prefix if the change has no user-visible impact (API, test frameworks, etc.)
• Appropriate autotests or explanation to why this change has no tests
• For dependency updates: links to external changelogs and, if possible, full diffs

Desired reviewers

@jenkinsci/java11-support

[MarkEWaite]

I read the changelog and all the changes seem reasonable to me.