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.
This is breaking change where bigint and bigserial Postgres types will be encoded as GraphQL String types, as opposed to Int as present in earlier releases.
Input types were already encoded as String.
This is achieved by selecting `bigint` and `bigserial` columns as `text`s in the SQL query: `select "big_id"::text ..` instead of `select "big_id" .. `.
Reason for that change is outlined in #633 where JavaScript cannot decode 64 bit Integers.
