change from 4 to 2 planar reflection HDRP by default

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/LightLoop/GlobalLightLoopSettings.cs

         public int pointCookieSize = 128;
         public int cubeCookieTexArraySize = 16;
 
-        public int reflectionProbeCacheSize = 4;
+        public int reflectionProbeCacheSize = 2;
         public int planarReflectionProbeCacheSize = 1024;
         public int reflectionCubemapSize = 128;
         public int planarReflectionTextureSize = 128;