Use CLI to configure max instances cache (#5177)

* Use CLI to configure max instances cache

* Fix tests

* Move default value into CLI

* Use SmallVec

* Apply review comments

* Get rid of `SmallVec`

Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/bin/node/testing/src/bench.rs

@@ -150,7 +150,7 @@ impl BenchDb {
 
 		let (client, backend) = sc_client_db::new_client(
 			db_config,
-			NativeExecutor::new(WasmExecutionMethod::Compiled, None),
+			NativeExecutor::new(WasmExecutionMethod::Compiled, None, 8),
 			&keyring.generate_genesis(),
 			None,
 			None,