[DOC] Add segment setting for tiered cache

[sgup432]

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• Request a change to existing documentation
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As part of segmented cache for tiered cache(opensearch-project/OpenSearch#16047), we are introducing a new setting for user to configure number of segments. We need to update existing tiered caching doc to include this setting.
Also add disk cache alias setting. And size setting.
Add tiered disk cache storage path
Correct indices.request.cache.tiered_spillover.disk.store.policies.took_time.threshold to indices.requests.cache.tiered_spillover.disk.store.policies.took_time.threshold

*Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.
2.18

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