Allow Egress to Be Configured to Save Track Metadata

[jezell]

When recording tracks, often additional information is required to be able to make use of the tracks for transcription, compositing, etc. If egress could be configured to drop down a .json file with some track information next to the track, it would be very useful, as some of these scenarios can't be accomplished with knowing some basic information like the offset of the track from the start (in relation to the other tracks in the room), the track info (id, name, source, etc.), participant info, the room info.

In the future, this metadata could be used by a recordings service to allow enumerating recordings for a room along with some basic metadata about the tracks.

[frostbyte73]

Added in #127