fix(reranking): uses semantic search score

[massi-ang]

Fills up the documents returned by the retriever with the top scored semantic search documents

Issue #, if available:

Fix #197

Description of changes:
The fill-up logic is changed so:

• only selects records that have a semantic search score and ignore other records
• for aurora takes into consideration that "inner" metric produces negative values
• correctly implements the filtering of the top-k items

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