Drop these in mu-plugins

remote-media-loader.php

<?php

/**
 * Plugin name: Remote Media Loader
 * Description: Save local storage space by mapping you /uploads directory to your staging or production site
 * Author: Axl Crawford
 * Author uri: https://www.barques.co.uk/
 * License: MIT
 */

// Exclude http://
$local_url = "myproject.local"; 
// Include http:// or https://
$remote_url = "https://myproject.dev";

if ( $local_url === $_SERVER['HTTP_HOST'] ){
	add_filter( 'upload_dir', function ( $uploads ) {
		$uploads['baseurl'] = "$remote_url/wp-content/uploads";

		return $uploads;
	} );
}