try-runtime: run migration checks per default (#13684)

* try-runtime: run migration checks per default

The current behaviour of having to explicetly specify --checks seems
to cause confusion. Therefore bringing back the old behaviour of
running the pre- and post-upgrade checks per default.

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Fix docs

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

---------

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

substrate/utils/frame/try-runtime/cli/src/commands/on_runtime_upgrade.rs

@@ -40,8 +40,8 @@ pub struct OnRuntimeUpgradeCmd {
 	/// Performing any checks will potentially invalidate the measured PoV/Weight.
 	// NOTE: The clap attributes make it backwards compatible with the previous `--checks` flag.
 	#[clap(long,
-		default_value = "None",
-		default_missing_value = "All",
+		default_value = "pre-and-post",
+		default_missing_value = "all",
 		num_args = 0..=1,
 		require_equals = true,
 		verbatim_doc_comment)]