[JENKINS:SECURITY-2180] Incorrect permission checks in `matrix-auth` may allow accessing some items

Items (like jobs) can be organized hierarchically in Jenkins, using the Folders Plugin or something similar.
An item is expected to be accessible only if all its ancestors are accessible as well.

matrix-auth 2.6.5 and earlier does not correctly perform permission checks to determine whether an item should be accessible.

This allows attackers with Item/Read permission on nested items to access them, even if they lack Item/Read permission for parent folders.

matrix-auth 2.6.6 requires Item/Read permission on parent items to grant Item/Read permission on an individual item.

As a workaround in older releases, do not grant permissions on individual items to users who do not have access to parent items.

In case of problems, the link:/doc/book/managing/system-properties/[Java system property] hudson.security.AuthorizationMatrixProperty.checkParentPermissions can be set to false, completely disabling this fix.