fix: handle arrays properly in FormData

When FormData contains arrays (e.g., multiple file uploads), the current
implementation incorrectly stringifies the entire array instead of
appending each item individually.

This fix:
- Detects when a property is an array
- Iterates through each array item
- Properly appends each file/blob individually to FormData
- Preserves non-file array items by JSON.stringify-ing them individually

This enables proper multi-file uploads and array handling in FormData,
which is essential for APIs that accept multiple attachments or files.

Author: omarmciver

templates/base/http-clients/fetch-http-client.ejs

@@ -113,14 +113,12 @@ export class HttpClient<SecurityDataType = unknown> {
 
             return Object.keys(input || {}).reduce((formData, key) => {
                 const property = input[key];
-                formData.append(
-                    key,
-                    property instanceof Blob ?
-                        property :
-                    typeof property === "object" && property !== null ?
-                        JSON.stringify(property) :
-                    `${property}`
-                );
+                const propertyContent = property instanceof Array ? property : [property];
+
+                for (const formItem of propertyContent) {
+                    const isFileType = formItem instanceof Blob || formItem instanceof File;
+                    formData.append(key, isFileType ? formItem : JSON.stringify(formItem));
+                }
                 return formData;
             }, new FormData());
         },