Place holder support At other Areas

## Is your enhancement request related to a problem? Please describe

field Place holder is a good place for educating your user in how to use product. Currently are placeholder for question tile. Request to add other placeholders in following order of priority

1. Question body (I can educate user how to write good question)
2. Answer Body (I can educate user how to write good answer)
3. comment body (least priority - I can ask user to be polite, be respectfull etc)

## Describe the solution you'd like

A clear and concise description of what you want to happen.

## Describe alternatives you've considered

A clear and concise description of any alternative solutions or features you've considered.

首先定位问题卡片现有的占位符，并追踪其文本的配置和渲染方式。按照请求的优先级顺序，将相同的流程扩展到问题正文、回答正文和评论正文，然后验证每个编辑器是否显示其已配置的占位符。

由索引模型根据 Issue 内容生成。