add support for a `/media` persistent storage type

[haydnv]

should support media types:

• JSON
• HTML
• JavaScript
• PDF
• JPG/PNG/SVG/GIF
• AAC audio
• MP4 video

with an appropriate MIME types if a media object is requested by itself (it can be replaced with a Link if requested as part of a larger document). JSON, HTML, and JavaScript should be convertible with a String and validated with destream_json, swc_html_parser, and swc_ecma_parser, respectively. PDFs should be convertible to an image using pdf_render. Images, audio, and video should be convertible with a Tensor or Stream of Tensors using image and gstreamer.

These can be implemented as-needed.