Feature: Add subsample option to obp.dataset.OpenBanditDataset

[usaito]

new feature

• add sample_size option to the sample_bootstrap_bandit_feedback method of obp.dataset.OpenBanditDataset
  

  zr-obp/obp/dataset/real.py

  Lines 281 to 283 in e85ba78

  	def sample_bootstrap_bandit_feedback(
  	self,
  	sample_size: Optional[int] = None,

This works as follows.

tests

• added some tests wrt the new feature in test_real.py

refactor

• allow string as the input of data_path as follows

• fix some english expressions in the docstring

[fullflu]

I’m sorry for the delayed response. LGTM other than the [imo] point!

[usaito]

@fullflu Thanks for your review!