Per-message ProviderScope for Websockets

It looks like `ProviderScope.Session` is kept on memory for the whole ws life, while instead I need to create a new instance on each ws message in order to be able to use Mikro-ORM with graphql-modules and ws transport: https://github.com/accounts-js/accounts/pull/1003#issuecomment-651710092

I'm creating an Accounts.js adapter for Mikro-ORM and I would like to share the same `EntityManager` provider (which takes care of forking it on each network request/ws message) with the Accounts.js authentication module, so that the Identity Map gets shared.

Is there anything graphql-modules provides in order to restric the lifespan to ws messages when using a ws transport?