Add a generic rescorer retriever based on the search request's rescore functionality

[jimczi]

This pull request introduces a new retriever called rescorer, which leverages the rescore functionality of the search request.
The rescorer retriever re-scores only the top documents retrieved by its child retriever, offering fine-tuned scoring capabilities.

All rescorers supported in the rescore section of a search request are available in this retriever, and the same format is used to define the rescore configuration.

Example:

  - do:
      search:
        index: test
        body:
          retriever:
            rescorer:
              rescore:
                window_size: 10
                query:
                  rescore_query:
                    rank_feature:
                      field: "features.second_stage"
                      linear: { }
                  query_weight: 0
              retriever:
                standard:
                  query:
                    rank_feature:
                      field: "features.first_stage"
                      linear: { }
          size: 2

Key Changes

1. Rescore Phase Adaptation:
   The original rescore phase was modified to support tie-breaking on the _shard_doc field. This ensures consistent sorting across all rounds of rescoring.
2. CompoundRetrieverBuilder Integration:
   The implementation uses the CompoundRetrieverBuilder, ensuring the rescorer retriever can seamlessly integrate into any position within the retriever tree.

Commit Structure

• Commit 1: Adapts the rescore phase to handle _shard_doc as a tiebreaker.
• Commit 2: Implements the rescorer retriever.

To facilitate review, I split the changes into two commits. If preferred, I can open separate pull requests for each commit to simplify the review process. However, I opted to include all changes in this PR to provide a complete overview.

Closes #118327

[benwtrent]

Thank you for tackling this @jimczi ! I didn't fully review, but it looks nice!