Clone Context on each GraphQL subscription execution

[50U10FCA7]

Synopsis

Context in juniper_graphql_ws shared across multiple GraphQL subscriptions in same WebSocket connection, which causes problems with defining subscription-local data.

Solution

Clone Context for each GraphQL subscription in WebSocket connection. It will allow end-user to control the context scope:

• If user still need to share context between multiple subscriptions - he just wraps the required data in Arc;
• If user need to strict context scope to be subsciption-local - he just reset the required data in impl Clone for Context.

Checklist

• Tests are added
• Documentation is added (including Book)
• CHANGELOG is filled

[50U10FCA7]

FCM

Clone `Context` for each GraphQL subscription in `juniper_graphql_ws` crate (#1369)

[50U10FCA7]

@tyranron Looks like I forgot to update trait bounds in tests. Can take the PR back to Draft to fix tests?