Track more detail about KeeServerUnreachableExceptions

[luckyrat]

e.g. if (e.error is SocketException && e.error.osError is OSError && e.error.osError.errorCode == 7) might let us ultimately inform the user about the specifics of why we couldn't connect to the Kee servers and thus narrow down the list of potential solutions.

Since 99.9% of issues are going to be resolved by just trying again later, this is not a high priority task but anyone that wants to take a look can start with where this exception is thrown and caught. E.g. in the DioHelperHandleException