[META] Enhance stability and sustainability of hybrid query

[martin-gaievski]

This meta issue tracks a series of feature requests and improvements aimed at making the current implementation of the hybrid query in the Neural Search plugin more stable and sustainable. The goal is to address the current non-standard implementation approaches that may be deprecated or break any time by introducing new extension points and features in the core OpenSearch repository

• [Feature Request] Add extension points for pre/post collecting scores in QueryPhase OpenSearch#17593 Extension points for pre/post collecting scores in QueryPhase
• [Feature Request] Add extension point to allow customizations and/or extensions in Rescore processor OpenSearch#16183 Extension point to allow customizations and/or extensions in Rescore processor
• [FEATURE] Allow custom serialization and deserialization for custom TopDocs implementation OpenSearch#9697 Serialization and deserialization for custom TopDocs implementation