Support merge policy settings like index.merge.policy.max_merged_segment

[onyxmaster]

Hi!

Previous version of the driver supported merge policy descriptors, including index.merge.policy.max_merged_segment. Nowadays, the only merge parameters that are supported are minimum/maximum segments for scheduler, forcing the merging policy to be customized by an external tool, after the index creation. This looks like an oversight to me, especially since kNN documentation explicitly recommends tuning this parameter for large indices.

Thank you.