fix: AWS4 authentication method didn't sign request body (#430)

Co-authored-by: Gregory Schier <gschier1990@gmail.com>

crates/yaak-plugins/src/events.rs

@@ -746,6 +746,7 @@ pub struct CallHttpAuthenticationRequest {
     pub method: String,
     pub url: String,
     pub headers: Vec<HttpHeader>,
+    pub body: Option<String>,
 }
 
 #[derive(Debug, Clone, Default, Serialize, Deserialize, TS)]