Add TestPanic feature flag (#34963)

Now the `dev: panic` action can be run on all release channels if the
user has the feature flag enabled.

Release Notes:

- N/A

crates/feature_flags/src/feature_flags.rs

@@ -85,6 +85,11 @@ impl FeatureFlag for ThreadAutoCaptureFeatureFlag {
         false
     }
 }
+pub struct PanicFeatureFlag;
+
+impl FeatureFlag for PanicFeatureFlag {
+    const NAME: &'static str = "panic";
+}
 
 pub struct JjUiFeatureFlag {}