Added test for CDN config for Subdir site (#713)

ref https://linear.app/ghost/issue/PRO-1517

- A site of example.com/blog with a UUID of 79a967d0-dc42-4623-a0b5-dffbd4193b40 still only has files at storage.ghost.io/c/79/a9/79a967d0-dc42-4623-a0b5-dffbd4193b40/content/files/ not storage.ghost.io/c/79/a9/79a967d0-dc42-4623-a0b5-dffbd4193b40/blog/content/files/

Author: vershwal

packages/url-utils/test/unit/utils/transform-ready-to-absolute.test.js

@@ -128,6 +128,19 @@ describe('utils: transformReadyToAbsolute()', function () {
             result.should.equal('https://site-base.com/content/media/video.mp4');
         });
 
+        it('converts media url with CDN and subdirectory in site URL', function () {
+            const storageCdn = 'https://storage.ghost.io/c/test-uuid';
+            const subdirSiteUrl = 'https://mysite.com/blog';
+            const options = {
+                staticMediaUrlPrefix: 'content/media',
+                mediaBaseUrl: storageCdn
+            };
+
+            const result = transformReadyToAbsolute('__GHOST_URL__/content/media/video.mp4', subdirSiteUrl, options);
+
+            result.should.equal('https://storage.ghost.io/c/test-uuid/content/media/video.mp4');
+        });
+
         it('uses CDN for media and site URL for files when only media CDN is configured', function () {
             const options = {
                 staticImageUrlPrefix: 'content/images',