Pass and merge subscription's event and query ctxs

[gastonmorixe]

When a subscription is triggered, there's an param to pass a context: but it's lost because it's not forwarded to the Subscription::Event.

Now when Subscription#execute_update is executed, we can now merge query's context with event's context.

This allows to pass an id of the sender of a query and compare it with the receiver of a subscription in the #update method, for example to prevent the sender of the subscription to receive its own updates by skipping it when the ids match.

Example:

module Subscriptions
  class ExampleSubscription < ::Types::Base::Subscription
    payload_type ::Types::ExampleSubscriptionPayload

    argument :model_id, ID, required: true, loads: ::Types::Models::MyModel, can_can_action: :read

    def subscribe(model:)
      super
    end

    def update(model:)
      # skip update when the sender is the same as the receiver of the update
      return :no_update if self.context[:client_id].present? && 
            self.context[:sender_client_id].present? && 
            self.context[:client_id] == self.context[:sender_client_id]

      super
    end
  end
end

MySchema.subscriptions.trigger(
   :my_update,
   # args:
   {
      model_id: "MODEL_ID"
   },
   # payload:
   {
      model: "MODEL_INSTANCE"
   },
   context: { sender_client_id: "SENDER_ID" }
)

[rmosolgo]

This looks great -- thanks for the fix!