Public API for is_maximizable_metric

[Innixma]

(Related Issue: #1890)
(CatBoost version v1.0.3)

Following the logic of this commit, to determine if a string eval_metric is_max_optimal==True I can do the following:

eval_metric = 'Accuracy'
from catboost._catboost import is_maximizable_metric
is_max_optimal = is_maximizable_metric(eval_metric)

I can also do:

from catboost import metrics
eval_metric = metrics.Accuracy()
is_max_optimal = eval_metric.is_max_optimal()

Given eval_metric = 'Accuracy', is there:

1. A way to do the same as is_max_optimal = is_maximizable_metric(eval_metric) without having to use a private API?

or

2. A way to convert this automatically to the catboost metric object catboost.metrics.Accuracy() via the string alone?

In general I want to avoid using a private API function.

[LyzhinIvan]

is_maximizable_metric and is_minimizable_metric are public now.