4-space indent selected text in description

https://ombulabs.atlassian.net/browse/DT-263

**Branch/Commit:**

Main branch

**Describe the feature:**

> **As a developer**
> **I select some lines from the description**
> **And then I click a button**
> **And I see the selected lines indented with 4 leading white spaces so it's formatted as a block**

**Problem:**

Currently, if we want to add code, we have two methods:
- triple backticks around the code (which is not always reliable and adds a color to the code)
- 4-spaces indentation (which is pretty annoying to adjust the indentation once the code is in the desription box or you have to update the indentation before copying the code)

**I will abide by the [code of conduct](CODE_OF_CONDUCT.md)**

从 main branch 中的描述框开始，找到作用于所选行的控件。验证当前如何处理选择和缩进，然后确认点击按钮会在所选行开头添加四个空格，并且生成的文本会被格式化为一个块。

由索引模型根据 Issue 内容生成。