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/client/executor/src/lib.rs

@@ -78,6 +78,7 @@ mod tests {
 			Some(8),
 			sp_io::SubstrateHostFunctions::host_functions(),
 			true,
+			8,
 		);
 		let res = executor.call_in_wasm(
 			&WASM_BINARY[..],