RpcHandlers Refactorings (#6846)

* allow access to the underlying Pubsub instance from RpcHandlers

* bump Cargo.lock

* no more Arc<RpcHandlers>

* bump Cargo.lock

* Debug,.

* Arc<RpcHandlers>

* RpcHandler

* RpcHandlers::io_handler

* remove chain spec from cli

* address pr comments

* remove stray newline

Co-authored-by: Ashley <ashley.ruglys@gmail.com>

Co-authored-by: Tomasz Drwięga <tomasz@parity.io>
Co-authored-by: Ashley <ashley.ruglys@gmail.com>