Merged PR 20846: Use helper to get scoped base media URL

## What's being changed

Fetching a product image URL for catalog sync, in `UrlFinder`.

## Why it's being changed

The current `getMediaUrl()` method to fetch a media URL for the small image only gets the URL set at default level. This is a problem for some merchants who set the default value to e.g. 'admin.site.com' and then have a firewall on that subdomain.

The `getSmallImageUrl()` helper method now in place is able to get the frontend URL for the supplied product, which is what we need for catalog insight data.

## How to review / test this change

- Set the Base Media URL for your Main Website to be different from the URL set at default
- Set catalog sync to run at Store level
- Run catalog sync
- Confirm that the 'imagePath' fields use the desired base media URL, and that the complete paths output are correct.
- Check that if catalog sync runs at default level, the default base media URL is used

## Notes

- In our testing we've noticed that the modified call outputs an image path with two slashes in it e.g. http://stuff.m19develop.local/media/catalog/product//m/s/msj000t_2.jpg. This appears to be core Magento behaviour and doesn't affect the resolution of the URL.
- Magento will use the base media URL of the first website to which the product belongs. e.g. if product X belongs to websites 2 and 3, the image path will use the base media URL of website 2.

Related work items: #113530

code/Dotdigitalgroup/Email/Model/Catalog/Urlfinder.php

@@ -43,9 +43,8 @@ public function getProductImageUrl($product)
             $product = $parentProduct;
         }
 
-        return Mage::getModel('catalog/product_media_config')
-            ->getMediaUrl($product->getSmallImage());
-
+        return Mage::helper('catalog/product')
+            ->getSmallImageUrl($product);
     }
 
     /**