Strict empty steps validation (#10041)

* Add two failings tests for strict empty steps.

* Implement strict validation of empty steps.

json/src/spec/authority_round.rs

@@ -56,6 +56,8 @@ pub struct AuthorityRoundParams {
 	pub empty_steps_transition: Option<Uint>,
 	/// Maximum number of accepted empty steps.
 	pub maximum_empty_steps: Option<Uint>,
+	/// Strict validation of empty steps transition block.
+	pub strict_empty_steps_transition: Option<Uint>,
 }
 
 /// Authority engine deserialization.