Allow setting a custom name for the upload-image input

[robinvandernoord]

Fix for #571.

By setting imageInputName you can customize the name of the input used by EasyMDE to upload images. By default it is set to 'image' as it was before.

new EasyMDE({element: document.getElementById('my-textarea'), imageInputName: "easyMDEImage", toolbar: ['upload-image']})

<input class="imageInput" type="file" multiple="" name="easyMDEImage" accept="image/png, image/jpeg, image/gif, image/avif" style="display: none; opacity: 0;">

[Ionaru]

Thank you for the PR!

You can use the new option in the @next version of the package, I'll do a proper release including documentation for the option soon. :)