rpc_module: SubscriptionSink::close -> SubscriptionSink::close_with_error

[niklasad1]

Close #1009

[jsdw]

Makes sense to me!

I'm not entirely sure we need close_with_result_notif (and as a nit I might have gone for close_with_error instead of close_with_error_notif) but all good :)

[niklasad1]

I'm not entirely sure we need close_with_result_notif (and as a nit I might have gone for close_with_error instead of close_with_error_notif) but all good :)

The reason I did it like that is that close_with_error isn't necessarily an error it may be like the subscription could be defined like without no message when it's "completed" for some reason. However, I would happy to remove those annoying names if that's clear enough now