Add config command (#5607)

* Add config command

* Format code

Co-authored-by: Frank Zhang <v-frankz@microsoft.com>

crates/nu-command/src/default_context.rs

@@ -315,6 +315,8 @@ pub fn create_default_context(cwd: impl AsRef<Path>) -> EngineState {
             LetEnv,
             LoadEnv,
             WithEnv,
+            ConfigNu,
+            ConfigEnv,
         };
 
         // Math