Handle CORS errors with client side GQL calls

[krzysztofwolski]

https://docs.saleor.io/docs/3.x/developer/extending/apps/developing-apps/troubleshooting#client-side-graphql-requests-are-rejected-due-to-cors-error

When the Cloud instance has CORS allow list set up, GQL calls the app iFrame will be blocked. Most of our communication is done server-side, but long-running jobs are affected by this issue.

Tasks

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1. Detect CORS-related errors in the app
2. Present a message to the user about why the operation cant be performed and how to change the cloud settings to resolve the issue
3. [To be discussed] CORS settings can be detected before the import operation is even triggered, so we can add banner on the main page of the app configuration