Add field to menu settings to output open graph image

I want to add a media-field to the menus settings to pick an image for each menu item and output this as open graph images. I see two options:

1. I add the field to the tab "Metadata" which then will be outputted via librariessrcDocumentRendererHtmlHeadRenderer.php. But i do not know where i can add fields to that tab.
2. I add the field in my custom (category blog) layout xml-file and then somehow get it in my template index.php but i do not know how to get access to the field there and documentation says:
   "Note that if you add new parameters, these can be used in the layout file but will not be used in the core model or view files."
   Would i somehow have to put my field in the layout file to use it in my index.php?