Fix: Allow empty Content-Type when no body (#1693)

[betawait]

By default Axios will set the Content-Type for POST/PUT/PATCH requests to "application/x-www-form-urlencoded" if the Content-Type header is not specified.

This explicitly sets the content type to "false" when there the body mode is set to "none", and the user has not set an explicit content type themselves. Setting the content type to false directs Axios not to send a Content-Type header.

Description

This PR fixes an issue where an unwanted Content-Type header would be added to a POST request with body mode set to "none". Axios adds "application/x-www-form-urlencoded" as the default Content-Type for POST/PUT/PATCH requests, unless the content type is explicitly set to 'false'.

If content-type is explicitly set by a user then that will still be preserved.

The interpolate-vars.js file had to be modified to handle content-type being set to 'false', as it was always expecting a string, and creating an empty string otherwise.

This is my first time in the bruno codebase, so I'm not confident I've thought about other side-effects this could have. I'm also not sure about bruno-cli. I would welcome any advice on other places to check.
 

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