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/lib.rs

@@ -62,7 +62,7 @@ pub use self::builder::{
 pub use config::{Configuration, Role, PruningMode, DatabaseConfig};
 pub use sc_chain_spec::{
 	ChainSpec, GenericChainSpec, Properties, RuntimeGenesis, Extension as ChainSpecExtension,
-	NoExtension,
+	NoExtension, ChainType,
 };
 pub use sp_transaction_pool::{TransactionPool, InPoolTransaction, error::IntoPoolError};
 pub use sc_transaction_pool::txpool::Options as TransactionPoolOptions;