Export more from sc-service (paritytech#5250)

Follow-up to paritytech#4457, looks
like more things were missing

---------

Co-authored-by: Niklas Adolfsson <niklasadolfsson1@gmail.com>
(cherry picked from commit cd1a29f)

prdoc/pr_5250.prdoc

@@ -0,0 +1,12 @@
+title: Export `MetricsService` and add public constructor to `RpcHandlers`
+
+doc:
+  - audience: Node Dev
+    description: |
+      `sc-service` was missing just a couple of things in public API in order to make it possible to recreate its
+      `spawn_tasks`, specifically `MetricsService` struct and `RpcHandlers` didn't have public constructor, which were
+      both finally addressed.
+
+crates:
+  - name: sc-service
+    bump: patch

substrate/client/service/src/builder.rs

@@ -508,7 +508,7 @@ where
 	};
 
 	let rpc = start_rpc_servers(&config, gen_rpc_module, rpc_id_provider)?;
-	let rpc_handlers = RpcHandlers(Arc::new(gen_rpc_module(sc_rpc::DenyUnsafe::No)?.into()));
+	let rpc_handlers = RpcHandlers::new(Arc::new(gen_rpc_module(sc_rpc::DenyUnsafe::No)?.into()));
 
 	// Spawn informant task
 	spawn_handle.spawn(

substrate/client/service/src/lib.rs

@@ -64,6 +64,7 @@ pub use self::{
 	},
 	client::{ClientConfig, LocalCallExecutor},
 	error::Error,
+	metrics::MetricsService,
 };
 #[allow(deprecated)]
 pub use builder::new_native_or_wasm_executor;
@@ -109,6 +110,11 @@ pub trait ClientExt<Block: BlockT, B: backend::Backend<Block>> {
 }
 
 impl RpcHandlers {
+	/// Create PRC handlers instance.
+	pub fn new(inner: Arc<RpcModule<()>>) -> Self {
+		Self(inner)
+	}
+
 	/// Starts an RPC query.
 	///
 	/// The query is passed as a string and must be valid JSON-RPC request object.