Add json+ld metadata

[dascritch]

see

• https://forum.dotclear.org/viewtopic.php?pid=336898
• https://jsonld.com/
• https://jsonld.com/video/
• https://schema.org/CreativeWork
• https://schema.org/sharedContent
• https://search.google.com/structured-data/testing-tool

and missing rss https://developers.google.com/search/docs/data-types/podcast