Custom width / height for export

### Feature Request Allow setting custom width and height of images for export. Presets for common social media platforms would also be a nice addition. ### Use Case Currently, to prevent Instagram from compressing the image too hard, I need to manually resize and compress images to 1080px on the longest side. Having a simple option to export for various social media platforms would make the export workflow much simpler and I wouldn't have to round trip through Photoshop at all.