[Star tree] Removing star tree indexing and queries added till 2.19 out of expermental

[bharath-techie]

Removing feature flag for star tree index and queries that are introduced by 2.19

Description

1. Indexing has remained same since 2.18 for the most part. And in 2.19 , we have support for date histogram, metric aggregations and term / terms / range query support. So removing feature flag protection for these features.
2. Still the newer queries and newer aggregations must be behind a feature flag - date range query, nested aggregations and boolean queries are yet to be merged. Have restricted terms aggs and range aggs in this PR. [ server/src/main/java/org/opensearch/search/startree/StarTreeQueryContext.java]
3. In both search (server/src/main/java/org/opensearch/search/DefaultSearchContext.java) and indexing validations (server/src/main/java/org/opensearch/index/compositeindex/datacube/startree/StarTreeValidator.java) , we first check for explicit index setting and if present, we use the value otherwise we fallback to cluster setting.
4. By default both the cluster setting "indices.composite_index.star_tree.enabled" and index setting "index.search.star_tree_index.enabled" are "true"

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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