New client api performGenericRequest allows for custom graphql errors

[Matt-st]

The GraphQL specification has gone through changes with regards to the error specification seen here. The specification refers to preferred and non preferred ways of representing errors. In the most recent specification update from 2018, extensions are used to hold extra information that organizations may need to make their error handling more robust. Many organizations have used GraphQL prior to the addition of extensions in 2018 and therefore have created custom Error objects for their GraphQL schema implementations. To make this graphql client more robust and gain the ability to handle GraphQL errors that don't follow the current specification I thought I would add a performGenericRequest that can handle custom error objects. Please review and share your thoughts.