Improve UX flow when network connection errors

[vanch3d]

Expected behaviour

When connection to the backend cannot be secured because of network errors, the user should be notified appropriately and certain operations (like creating a new adapter) should be restricted

Actual behaviour

At the moment, most of the error handling has been focusing on receiving errors (4xx or 5xx) from the backend. But the cases where the requests cannot even be sent due to network issues have not been covered.

The frontend, being a Single-Page Application and using React Query caching facilities, continues to render relatively appropriately. Some of the icons are not properly loaded but the caches still provide all the information to populate the React pages.

It includes accessing and interacting with forms, even if it means sending data through requests that are not operational.

There is not a single feedback about the connection status to the user until a cache becomes "stale" is fetched again and the failure of X retries triggers the error

To Reproduce

Access the frontend, navigate through the different pages (to make sure all the requests are accessed once and cached) then shut the backend down.

Alternatively, use the browser throttling capability to simulate "offline" behaviour.

Details

Originally posted by @vanch3d in #95 (comment)