increase amount of metadata stored on platform .meta files

[dmjacobsen]

The dockerv2 interface can address a manifest using the hashed identifier so long as both the hashing algorithm and repo are known.

Please include the location (registry-1.docker.io, for example), repo (library, dmjacobsen, ubuntu, etc), and algorithm (typically sha256, but just in case please keep track). This will make it possible to re-download the image manifest from the remote source just based on what is stored on disk. It is not clear if we'll be able to reconstruct tags from that, so the pulltags should also be included, though not trusted (as those may get out of date).

Thanks, Doug