【backup】feat: Add a new node empty-node as a placeholder node

[wangliang181230]

What this PR does / why we need it?

feat: Add a new node empty-node as a placeholder node
新增一个新节点 空节点 作为占位节点

Summary of your change

空节点不做任何操作，仅用于流程占位节点，常用于判断器的ELSE中占位使用。
工作流工具中，经常会碰到这种情况。

1. 有空节点前：

2. 有空节点后：

3. 其他界面展示：

Please indicate you've done the following:

• Made sure tests are passing and test coverage is added if needed.
• Made sure commit message follow the rule of Conventional Commits specification.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed.

[wangliang181230]

顺便优化：移除节点左侧标题的宽度 width: 69%，固定右侧按钮的宽度（注：使用min-width更保险）使左侧标题能够显示出更多字来。

[baixin513]

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