Allow specific name for file uploads.

upload-files.js

@@ -8,7 +8,7 @@ export const upload = function(superClass) {
      * @param {Object} opts Upload options
      * @returns Promise
      */
-    uploadFiles(url, files = [], data = {}) {
+    uploadFiles(url, files = [], data = {}, fileKey = '') {
       return new Promise((resolve, reject) => {
         const request = new XMLHttpRequest();
         const formData = new FormData();
@@ -49,7 +49,7 @@ export const upload = function(superClass) {
         });
 
         for (let i = 0; i < files.length; i++) {
-          formData.append(files[i].name, files[i]);
+          formData.append(fileKey ?? files[i].name, files[i]);
         }
 
         document.dispatchEvent(new CustomEvent('before-request', { detail: request, bubbles: true, composed: true }));