Add prometheus registry to transaction pool, with couple of initial metrics (#5657)

* make new contructor

* add metrics to txpool

* fix review

* fix doc comment

* change to counters

* Update client/transaction-pool/src/metrics.rs

Co-Authored-By: Max Inden <mail@max-inden.de>

* Update client/transaction-pool/src/metrics.rs

Co-Authored-By: Max Inden <mail@max-inden.de>

* Update client/transaction-pool/src/metrics.rs

Co-Authored-By: Max Inden <mail@max-inden.de>

* Update client/transaction-pool/src/lib.rs

Co-Authored-By: Max Inden <mail@max-inden.de>

* Update client/transaction-pool/src/lib.rs

Co-Authored-By: Max Inden <mail@max-inden.de>

* use dedicated wrapper

Co-authored-by: Max Inden <mail@max-inden.de>

substrate/utils/frame/rpc/system/src/lib.rs

@@ -236,7 +236,11 @@ mod tests {
 		let _ = env_logger::try_init();
 		let client = Arc::new(substrate_test_runtime_client::new());
 		let pool = Arc::new(
-			BasicPool::new(Default::default(), Arc::new(FullChainApi::new(client.clone()))).0
+			BasicPool::new(
+				Default::default(),
+				Arc::new(FullChainApi::new(client.clone())),
+				None,
+			).0
 		);
 
 		let source = sp_runtime::transaction_validity::TransactionSource::External;