[FEATURE] Add subscription in GraphQL

[omar2535]

Overview

Subscriptions are very different from normal Queries and Mutations. They use websockets instead of POST requests. This can also be a vector of attack, as possible leaks in message topics in a back-end implementation can often reveal sensitive information.

GraphQLer should be able to handle this as well, using context generated from the previous dependency-chain runs. For more resources:

• https://spec.graphql.org/October2021/#sec-Subscription
• https://graphql.org/blog/2015-10-16-subscriptions/
• https://daily.dev/blog/subscriptions-in-graphql

Implementation requirements

This will require some additional features to be done on both the compiler / fuzzer side. Namely, looking for subscription types, and using web-sockets to send subscription payloads.

Testing

Look for possible open-source APIs that already have subscriptions implemented. If not, create a test for this and add it to the integration tests.