UPDATE: I have created a video on sending multipart/form-data requests to explain this better.
Actually, Postman can do this.
Full example:
You DON’T need to add any headers, Postman will do this for you automatically.
Make sure you check the comment from @maxkoryukov
Be careful with explicit Content-Type header. Better – do not set it’s
value, the Postman is smart enough to fill this header for you. BUT,
if you want to set the Content-Type: multipart/form-data – do not
forget about boundary field.