Add new RPC method to get the chain type (#5576)

* Add new RPC method to get the chain type

This adds a new RPC method to get the chain type of the running chain.
The chain type needs to be specified in the chain spec. This should make
it easier for tools/UI to display extra information without needing to
rely on parsing the chain name.

* Update client/rpc-api/src/system/mod.rs

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Primitive crate

* Feedback

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

substrate/client/service/src/builder.rs

@@ -1016,6 +1016,7 @@ ServiceBuilder<
 				impl_name: config.impl_name.into(),
 				impl_version: config.impl_version.into(),
 				properties: chain_spec.properties().clone(),
+				chain_type: chain_spec.chain_type().clone(),
 			};
 
 			let subscriptions = sc_rpc::Subscriptions::new(Arc::new(tasks_builder.spawn_handle()));