Configurable resetting of request_id.

Ensuring that the request_id is reset to nil after processing a job is nice from a cleanliness perspective, but doesn't work properly if we want to have access to the request_id when an exception occurs, since the exception handling in sidekiq 2.17 is handled outside of the middleware chain.

This makes that behavior configurable, so it can be turned off by setting `Sidekiq::Middleware::Server::RequestId.no_reset = true`