Add multipart file upload for iOS

[sxcore]

This PR proposes a fix to problem when file uploads restarts completely when iOS app comes back from background state.

Summary

Added functions that will split files in part and safely check and save them on disk, and when starting again the remains of previous multipart files will be removed from disk to prevent unnecessary disk usage.

Compatibility

OS	Implemented
iOS	✅
Android	❌

Checklist

• [x] I have tested this on a device and a simulator
• [ ] I added the documentation in README.md
• [ ] I updated the typed files (TS and Flow)
• [ ] I've added Detox End-to-End Test(s)
• [ ] I've created a snack to demonstrate the changes: LINK HERE