Allow usage of dynamic values in Multipart Form

[barseghyanartur]

Is your feature request related to a problem? Please describe.
JSON works really nice, but when I switch to Multipart Form I can't dynamically set values.

Describe the solution you'd like
Allow usage of dynamic values in Multipart Form.

Describe alternatives you've considered
No alternatives, so far.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.