feat: add webhook body template and headers support for channels

k-tv-backend/domain/src/entities.rs

@@ -90,6 +90,8 @@ pub struct Channel {
     pub logo_opacity: f32,
     pub webhook_url: Option<String>,
     pub webhook_poll_interval_secs: u32,
+    pub webhook_body_template: Option<String>,
+    pub webhook_headers: Option<String>,
     pub created_at: DateTime<Utc>,
     pub updated_at: DateTime<Utc>,
 }
@@ -117,6 +119,8 @@ impl Channel {
             logo_opacity: 1.0,
             webhook_url: None,
             webhook_poll_interval_secs: 5,
+            webhook_body_template: None,
+            webhook_headers: None,
             created_at: now,
             updated_at: now,
         }