Add support to get best run and metrics that are zero-optimized

**Is your feature request related to a problem? Please describe.**
Our current `IsBestRun` method tries to find the best run for a given metric by finding the largest value. This works well for 99% or so of cases but e.g. log loss entropy should be closer to zero to be a good value.

**Describe the solution you'd like**
Add ability to define what a good run looks like for a given metric

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

**Additional context**
Add any other context or screenshots about the feature request here.