Implement brand image endpoints for APIv4 (#5733)

* Implement brand image endpoints for APIv4

* Fix unit test

i18n/en.json

@@ -151,6 +151,10 @@
     "id": "api.admin.upload_brand_image.too_large.app_error",
     "translation": "Unable to upload file. File is too large."
   },
+  {
+    "id": "api.brand.init.debug",
+    "translation": "Initializing brand API routes"
+  },
   {
     "id": "api.api.init.parsing_templates.debug",
     "translation": "Parsing server templates at %v"