[Extensions]Implement APIs to invoke extension points in SDK

[owaiskazi19]

Is your feature request related to a problem? Please describe.
Currently, the extension points which are integrated in the SDK are invoked only once when OpenSearch bootstraps. There should be a way to invoke these extension points as and when the plugin requires.

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[owaiskazi19]

Tracked via: opensearch-project/opensearch-sdk-java#315