Add debug logging for default catalog overwrite in SessionState build (#15251)

Co-authored-by: Kermit <[email protected]>

Author: byte-sourcerer

datafusion/core/src/execution/session_state.rs

@@ -1415,10 +1415,14 @@ impl SessionStateBuilder {
                 &state.runtime_env,
             );
 
-            state.catalog_list.register_catalog(
+            let existing_default_catalog = state.catalog_list.register_catalog(
                 state.config.options().catalog.default_catalog.clone(),
                 Arc::new(default_catalog),
             );
+
+            if existing_default_catalog.is_some() {
+                debug!("Overwrote the default catalog");
+            }
         }
 
         if let Some(analyzer_rules) = analyzer_rules {