Only applies r.MotionBlur.HalfResGather=1 on low and medium scalability settings

#rb trivial
#jira none
#preflight 61f8242da6632a34f34bc425

#ROBOMERGE-AUTHOR: guillaume.abadie
#ROBOMERGE-SOURCE: CL 18793536 in //UE5/Release-5.0/... via CL 18793702 via CL 18794553
#ROBOMERGE-BOT: UE5 (Release-Engine-Test -> Main) (v908-18788545)

[CL 18795039 by guillaume abadie in ue5-main branch]

Engine/Config/BaseScalability.ini

@@ -317,6 +317,7 @@ r.Lumen.Reflections.DownsampleFactor=1
 
 [PostProcessQuality@0]
 r.MotionBlurQuality=0
+r.MotionBlur.HalfResGather=1
 r.AmbientOcclusionMipLevelFactor=1.0
 r.AmbientOcclusionMaxQuality=0
 r.AmbientOcclusionLevels=0
@@ -337,6 +338,7 @@ r.Tonemapper.Quality=0
 
 [PostProcessQuality@1]
 r.MotionBlurQuality=3
+r.MotionBlur.HalfResGather=1
 r.AmbientOcclusionMipLevelFactor=1.0
 r.AmbientOcclusionMaxQuality=60
 r.AmbientOcclusionLevels=-1
@@ -369,6 +371,7 @@ r.DOF.Kernel.MaxBackgroundRadius=0.006   ; required because low gathering and no
 
 [PostProcessQuality@2]
 r.MotionBlurQuality=3
+r.MotionBlur.HalfResGather=0
 r.AmbientOcclusionMipLevelFactor=0.6
 r.AmbientOcclusionMaxQuality=100
 r.AmbientOcclusionLevels=-1
@@ -403,6 +406,7 @@ r.DOF.Kernel.MaxBackgroundRadius=0.012   ; required because of AccumulatorQualit
 
 [PostProcessQuality@3]
 r.MotionBlurQuality=4
+r.MotionBlur.HalfResGather=0
 r.AmbientOcclusionMipLevelFactor=0.4
 r.AmbientOcclusionMaxQuality=100
 r.AmbientOcclusionLevels=-1
@@ -439,6 +443,7 @@ r.DOF.Kernel.MaxBackgroundRadius=0.025
 
 [PostProcessQuality@Cine]
 r.MotionBlurQuality=4
+r.MotionBlur.HalfResGather=0
 r.AmbientOcclusionMipLevelFactor=0.4
 r.AmbientOcclusionMaxQuality=100
 r.AmbientOcclusionLevels=-1