Feat: Redesign and refactor agent module (#9113)

### What problem does this PR solve?

#9082 #6365

<u> **WARNING: it's not compatible with the older version of `Agent`
module, which means that `Agent` from older versions can not work
anymore.**</u>

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

rag/nlp/search.py

@@ -384,7 +384,7 @@ class Dealer:
         zero_vector = [0.0] * dim
         sim_np = np.array(sim)
         if doc_ids:
-            similarity_threshold = 0 
+            similarity_threshold = 0
         filtered_count = (sim_np >= similarity_threshold).sum()    
         ranks["total"] = int(filtered_count) # Convert from np.int64 to Python int otherwise JSON serializable error
         for i in idx:
@@ -403,7 +403,7 @@ class Dealer:
                     ranks["doc_aggs"][dnm]["count"] += 1
                     continue
                 break
-                
+
             position_int = chunk.get("position_int", [])
             d = {
                 "chunk_id": id,