[ENH] Turn on spann by default

Author: sanketkedia

rust/frontend/sample_configs/distributed.yaml

@@ -46,4 +46,4 @@ scorecard:
       - "collection_id:*"
     score: 100
 enable_span_indexing: true
-default_knn_index: "hnsw"
+default_knn_index: "spann"

rust/frontend/sample_configs/tilt_config.yaml

@@ -54,4 +54,4 @@ scorecard:
 circuit_breaker:
   requests: 1000
 enable_span_indexing: true
-default_knn_index: "hnsw"
+default_knn_index: "spann"