[Observability] Update required field from 'score' to 'scores' (#203584)

Closes #203739

## Summary

fix error: `“Error scoring documents: Tool call arguments for score were
invalid”`

[Observability] Update required field from 'score' to 'scores' in
scoreSuggestions schema

x-pack/platform/plugins/shared/observability_solution/observability_ai_assistant/server/utils/recall/score_suggestions.ts

@@ -102,7 +102,7 @@ export async function scoreSuggestions({
           type: 'string',
         },
       },
-      required: ['score'],
+      required: ['scores'],
     } as const,
   };