Is your feature request related to a problem? Please describe.

Yes.
When fetching and sending data as form data, the user is required to manually build a form data object.

• If the data is nested, building form data isn't trivial, and can result in an inappropriate structure and bugs.
• If the data already exists as an object or array, the user needs to write his own solution to convert an object to form data.

Describe the solution you'd like

Provide a reliable easy way to convert object to form data.

Describe alternatives you've considered

I couldn't find a simple existing solution to easily convert a nested object to form data.

Additional context

Since form data is only used (as far as I know) in the context of fetching, I thought Axios should provide this functionality. Perhaps export a function that can convert an object to form data, or add a property to AxiosConfig and handle the conversion internally.

If relevant I'd be happy to submit a PR.