Support testing GraphQL Subscriptions

Problem

GraphQL has three operation types that can accept arguments (input) and are good targets for testing: Queries, Mutations, and Subscriptions. API Security currently supports Queries and Mutations, but not Subscriptions. Subscriptions work via web sockets, which are HTTP connections that are promoted into a web-socket which then allows two-way communication similar to a TCP connection. API Security doesn't currently have support for web sockets.

Supporting Subscriptions will flush out our support for the testable aspects of GraphQL.

The majority of the work needed to support for GraphQL Subscriptions is in adding web-socket support to API Security. Once that has been done, testing subscriptions is straight forward.