Increase maxMergeAtOnce parameter in OpenSearch 3.0

[msfroh]

Is your feature request related to a problem? Please describe

There's a Lucene issue merged post-10.0 (apache/lucene#266) to increase the default maxMergeAtOnce parameter.

It (probably) can't go into Lucene 10 because it would be a surprising breaking change that can only come with a major version bump, so it's currently listed as a change that will go out with Lucene 11 (whenever that happens).

Describe the solution you'd like

Since we haven't released OpenSearch 3.0 yet, we still have the opportunity to pull this into our next major version.

If it's a better default then it shouldn't need to wait until OpenSearch 4.0.

Related component

Indexing:Performance

Describe alternatives you've considered

Wait until it becomes the default in Lucene 11.

Additional context

No response