Faraday 1.x can bypass Diplomat::QueryAlreadyExists

[tlbraams]

Faraday 1 made changes to the Faraday::ClientError, introducing Faraday::ServerError (https://github.com/lostisland/faraday/blob/main/UPGRADING.md#errors)

This split the errors, with client errors now responsible for 4xx codes and server errors for 5xx codes.
The Diplomat::Query#create method only expects/handles client errors. As such, (some) errors that were previously caught and reported as Diplomat::QueryAlreadyExists, now raise Faraday::ServerError.

[pierresouchay]

@tlbraams what would you suggest? Do you feel doing a PR?

Regards