Enable ModelFileManager to upload multiple files

[nlathia]

Also (in case this is something you would like to add) we found that we wanted to upload multiple files under a single model, whereas the ModelFileManager manager only supported uploading a single model from disk, so we added support as follows for that:

https://mlops-community.slack.com/archives/C0227QJCDS8/p1690742403031109?thread_ts=1690721464.955749&cid=C0227QJCDS8