Changes compared to `/v1alpha1/graphql`
* Changed all graphql responses in **/v1/graphql** endpoint to be 200. All graphql clients expect responses to be HTTP 200. Non-200 responses are considered transport layer errors.
* Errors in http and websocket layer are now consistent and have similar structure.
Rename the admin secret key header used to access GraphQL engine from X-Hasura-Access-Key to X-Hasura-Admin-Secret.
Server CLI and console all support the older flag but marks it as deprecated.
