feat: add support for custom image size file names (#7637)

Add support for custom file names in images sizes

```ts
{
  name: 'thumbnail',
  width: 400,
  height: 300,
  generateImageName: ({ height, sizeName, extension, width }) => {
    return `custom-${sizeName}-${height}-${width}.${extension}`
  },
}
```

docs/upload/overview.mdx

@@ -168,6 +168,22 @@ When an uploaded image is smaller than the defined image size, we have 3 options
   Use the `withoutEnlargement` prop to change this.
 </Banner>
 
+#### Custom file name per size
+
+Each image size supports a `generateImageName` function that can be used to generate a custom file name for the resized image.
+This function receives the original file name, the resize name, the extension, height and width as arguments.
+
+```ts
+{
+  name: 'thumbnail',
+  width: 400,
+  height: 300,
+  generateImageName: ({ height, sizeName, extension, width }) => {
+    return `custom-${sizeName}-${height}-${width}.${extension}`
+  },
+}
+```
+
 ### Crop and Focal Point Selector
 
 This feature is only available for image file types.