Move models in separate projects

rag-api-models/Requests/SearchRequest.cs

@@ -0,0 +1,9 @@
+namespace Rag.Models.Requests
+{
+    public sealed class SearchRequest
+    {
+        public required string QueryText { get; init; }
+        public IReadOnlyList<string>? TargetDocumentTypes { get; init; }
+        public int? TopK { get; init; }
+    }
+}