* represent all content as artifact.OCI interface and manipulate/add all content using oci layouts
* initial brew taps and macos universal binary
* change mediaType to string for better compatibility with other libraries
* ensure config is minimally viable for file/charts
* add transparent layer caching (filesystem) to artifact operations, clean up layer interface used by file/chart
* add store list and store copy commands
Signed-off-by: Josh Wolf <josh@joshwolf.dev>