Add User-Agent header to our NeopetsMediaArchive requests

Note: I validated this was working by temporarily changing the URI to
`https://echo.free.beeceptor.com`, which echoes the headers back, then
called `NeopetsMediaArchive.load_file_from_origin` directly.

app/services/neopets_media_archive.rb

@@ -72,7 +72,9 @@ module NeopetsMediaArchive
     # We use this in the `swf_assets:manifests:load` task to perform many
     # requests in parallel!
     Sync do
-      response = INTERNET.get(uri)
+      response = INTERNET.get(uri, [
+        ["User-Agent", Rails.configuration.user_agent_for_neopets],
+      ])
       if response.status != 200
         raise ResponseNotOK.new(response.status),
           "expected status 200 but got #{response.status} (#{uri})"