Better error messaging for max file size limit

[solocommand]

Ref JIRA CS-4336

When uploading an image over 1.5MB in size (via the Apollo FileUpload), the Rancher nginx server (load balancer) throws an HTTP 413 due to the payload being sent.

• Update error messaging when encountering this condition
• Ensure that GraphQL is handling and responding to this condition, not nginx.