Apollo Playground incorrectly formats form-data when using many Uploads
### Issue Description

When trying to implement a complex mutation that would combine multiple graphql-upload files I noticed that the Playground was incorrectly formatting form-data making it impossible for the server to understand what i wanted. I have provided a playground which covers most use cases with trying to upload files with GraphQL.

I am especially interested in tests 7 and 8 because they seem like they should work.
Other tests seem to fail because Playground prefixes file variables with index thinking it is a batch operation.
If i manually remove those prefixes the server is able to process the request.
Here is example of doing test 11 in Postman
[Postman Screenshot](https://pasteboard.co/3p8NYyXLM6BN.png)
I have also tested in Altair Client and it works aswell
[Altair Screenshot](https://pasteboard.co/0cLVx0L8ZGSb.png)

Maybe I am misunderstanding some kind of a limitation but I hope my tests will be useful in fixing this issue.
Ideally I was looking towards test 14 working because it would come extremely handy for example for user registration which includes a combination of required and optional single files and required and optional multi files as well as normal fields.
Thank You.

### Link to Reproduction

https://codesandbox.io/p/sandbox/quirky-alex-kjwhvx

### Reproduction Steps

Open the sandbox and execute test mutations using the apollo playground.
Upload any test files depending on what the test is for.