Implement auth error types for GraphQL

[ldclakmal]

Description:
This is to track the implementation of auth error types for GraphQL which will be used in context initialization phase and can be used in resolver phase as well.

Here is the summary of HTTP status codes.

Error type	Status code
Resolver level error	400
Context init level errors	500
Context init level custom errors	400

So, with the GraphQL proposal of security story [1] we will be adding 2 new error types as graphql:AuthnError and graphql:AuthzError and those will return the 400 status code responses.

[1] #1771