add more attributes to sequencing files etag and aws-s3 object URI

[sergpolly]

@Snehal1894 - that's what we've talked about regarding cLIMS improvements:

1. add etag as an attribute to a sequencing file (etag is a type of hashsum Amazon is using for S3 objects -files)
2. add alternative_path as an attributes to a sequencing file (not sure if there every be several alternative paths) - maybe just call it s3_uri - same things we need this to be able to track the location of files on Amazon and eventually even be able to use them for mapping (on Amazon or on our cluster)

Could you just look into that - see if it's easy/hard to modify the model accordingly ? would they brake anything potentially ? - just to make sure...