Open links outside iframe

Mirrors https://github.com/mckinsey/vizro/pull/845/

custom_components.py

@@ -57,7 +57,9 @@ class Markdown(vm.VizroBaseModel):
 
     def build(self):
         """Returns a markdown component with an optional classname."""
-        return dcc.Markdown(id=self.id, children=self.text, dangerously_allow_html=False, className=self.classname)
+        return dcc.Markdown(
+            id=self.id, children=self.text, dangerously_allow_html=False, className=self.classname, link_target="_top"
+        )
 
 
 class FlexContainer(vm.Container):