Action proposal: Send Request with a `JSON String`

### Description The operation of initiating a POST request that comes with the shortcut command is too cumbersome. It requires setting each field of the request body in the dictionary (which is very time-consuming and troublesome to operate). It would be much simpler if the request header and request body could be configured through a JSON string and then the request could be initiated. Moreover, you can also insert the variables of the shortcut instructions mentioned above into the JSON string, which makes it more flexible ～ <img width="676" height="572" alt="Image" src="https://github.com/user-attachments/assets/43439753-adf2-4231-8cd2-54667aaa8614" />