pbutils: Add support caps to RFC6381-codecs conversion
Submitted by Yeongjin Jeong
'codecs' is information for media stream, conforming to RFC-6381.
This is useful for information which creates Live streaming protocol metadata such as M3U8 master playlist or MPD manifest.
Because, some media player framework such as MSE (Media Source Extensions) need more information 'rfc6381-codecs' to test support for in the current browser.