Implement basic metrics layout & total elapsed time (#1250)

* Initial metadata processing

* Dynamic coloring and other stuff

* Use -vv / --meta

* More testing

* Cleanup

* Tweek message

Co-authored-by: Jakub Roztocil <jakub@roztocil.co>

httpie/plugins/base.py

@@ -155,3 +155,11 @@ class FormatterPlugin(BasePlugin):
 
         """
         return content
+
+    def format_metadata(self, metadata: str) -> str:
+        """Return processed `metadata`.
+
+        :param metadata: The metadata as text.
+
+        """
+        return metadata