Add optional metadata attribute to Dataframe container (#661)
Add optional metadata attribute to Dataframe container (#661)

Co-authored-by: Hussein Khalifa <0d2204e14d929f0e2cada5bb8e127e59b79e609b@google.com>
log2timeline/dftimewolf,Onager/dftimewolf,log2timeline/dftimewolf,Onager/dftimewolf