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

[aslotte]

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.

[Brett-Parker]

@aslotte what is your thinking here? To have an overload method for GetBestRun where the user can request what the metric is based on, e.g closest to 0 (ascending), closest to 1 (descending)? E.g return the log loss entropy (closest to 0). Or something else....

Current - public Run GetBestRun(Guid experimentId, string metricName)
Possible overload - public Run GetBestRun(Guid experimentId, string metricName, int closerTo)

Could also change the current method, or add our own logic, if metric = logloss = ascending etc....