Store HTTP request json body as a string

[Devessier]

Variables can be used without surrounding quotes.

The formatting is also preserved for raw json.

We would have to do additional work if we want to add other types of bodies, like form data.

Demo

https://github.com/user-attachments/assets/498dd9c8-6654-4440-9ab0-35bad5e34ca8

Closes https://github.com/twentyhq/core-team-issues/issues/1129

Related to https://github.com/twentyhq/core-team-issues/issues/1117. Doesn't solve the issue for webhooks but does for http body input.