Feature/many multipart file

[MuhmdHsn313]

New Pull Request Checklist

• I have read the Documentation
• I have searched for a similar pull request in the project and found none
• I have updated this branch with the latest develop to avoid conflicts (via merge from master or rebase)
• I have added the required tests to prove the fix/feature I am adding
• I have updated the documentation (if necessary)
• I have run the tests and they pass

This merge request fixes / refers to the following issues: there is no way to upload many multipart-file in the same form key in fromMap function, support to adding a list of

Pull Request Description

Support many multipart-file in the same form key in fromMap function you can see this feature in postman, I mean you can select many files in one field, I write and test my code without writing a unit test and it's working correctly, and added functions that help with adding & removing values from FormData.

[AlexV525]

Hi @MuhmdHsn313, can you add tests for the requests to make sure if multi files worked in the FormData? The change itself is less readable without proper tests and comments.

[AlexV525]

We've made our hardfork repo public and published a new version of dio, named diox.
If you're willing to continue on the PR, you can consider submitting it to https://github.com/cfug/diox.
You can also see why we're working for a hardfork at cfug/diox#29 and #1607.