[JENKINS-34254] Fix 'crumb missing' form

[daniel-beck]

See JENKINS-34254.

This is currently just a rebased #2268.

Jenkins currently breaks in this way and makes some built-in features plain unusable with enabled CSRF protection (which is the default since 2.0, ~19 months ago, and nobody should be disabling this anyway!).

Proposed changelog entries

• Make the 'Retry with POST' form work when CSRF protection is enabled.

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

[jglick]

#3187 looks better to me.

[daniel-beck]

Closing in favor of #3187.