Improve RAG debugging in backend

[anada10]

Currently backend logs are not good for RAG retrievals. Need to show it more like this

6/k payloads were retrieved
{chunkId: 1232143213213432
  parentName: elon_tweets
  chunkText: "i love bears"
  chunkRank: 1
  chunkStrategy: semantic/character/message
  chunkCosineScore: 0.92
  chunkTokens: 8
  chunkCreatedDate: utc timestamp
  topK: 10
   embeddingModel: bge/small   
     metadata {
       dateTweeted: 12/12/22
       length: 123232
       ...
     }
}

Users should also be able to see retrieval stats at a chunk level