Document remote monitoring cluster version requirement for upgrades?

We have a note here on version dependency, i.e. they can't do an export from a 6.x cluster to a 5.x monitoring cluster during upgrades: https://www.elastic.co/guide/en/x-pack/current/monitoring-production.html#monitoring-production

The problem is that this note is in the "setup" section of the monitoring guide and users are unlikely going to revisit this page as part of the upgrade. It will be helpful if we can call this out (or cross link) as part of the stack upgrade documentation.

从链接的版本依赖关系部分中的 monitoring production guide 开始，然后找到 issue 中引用的 stack upgrade 文档。记录或交叉链接以下要求：export 不能从 6.x 集群迁移到 5.x monitoring 集群，并确认升级指南已将这一点明确展示给用户。

由索引模型根据 Issue 内容生成。