The Call REST service microflow action allows you to upload a file.
Note that you may send attribute values as URL parameters if the service supports this.
See https://docs.mendix.com/refguide/call-rest-action#4-2-binary-for-the-entire-request
If you need to send a multipart request, you will need to use the REST services appstore module.
See https://github.com/mendix/RestServices#sending-and-receiving-files