Add meta command for the config subcommands (#5616)

When using `config` without the `config nu` or `config env` subcommands
introduced by #5607 display basic usage like `str`.

crates/nu-command/src/default_context.rs

@@ -317,6 +317,7 @@ pub fn create_default_context(cwd: impl AsRef<Path>) -> EngineState {
             WithEnv,
             ConfigNu,
             ConfigEnv,
+            ConfigMeta,
         };
 
         // Math