feat: improve restConnector error handling

[kwonoh]

The Rust server sends error messages to the client if the query fails (e.g., SQL syntax error, incorrect column name).
However, the current restConnector does not handle the error message from the server and tries to parse the response just based on the request type.

This PR adds a check whether the response was successful. If the response is not ok, then it throws an error with the response text that contains the error messages from the server.

With this change, queryError receives an Error instance with the error message from the server.

The error message format could be improved.

[domoritz]

Thank you. Looks good and throwing an error will reject the promise.