Add runtime measure to metainfo

[fstermann]

As suggested in the instructions

modelInfo(model.xgb)
#> $training.time.sec
#> [1] 15

we might want to include the runtime of different operations. I think it would be good to also include this for Predictions as well.

In my opinion this also fits in the metainfo category, which is why we could also store it there.

Tasks

• [ ] Figure out naming convention and preciseness
  • training.time.sec suggests the training time
  • We might also want to measure time it takes to predict
  • Have this be prediction.time.sec ?
  • Having only int seconds might not be optimal for fast algorithms
  • Maybe specify 100ms as well, e.g. 15,123 ?
• Implement runtime measure
  • [ ] For Training
  • [ ] For Prediction
  • [ ] For Resampling Prediction (Maybe the above can be reused)