Add experimental tune SSIM option to improve SSIM BDR

Docs/Parameters.md

Source/API/EbDebugMacros.h

Source/API/EbSvtAv1Enc.h

Source/App/EncApp/EbAppConfig.c

Source/Lib/Common/Codec/EbDefinitions.h

Source/Lib/Encoder/ASM_AVX2/CMakeLists.txt

Source/Lib/Encoder/ASM_AVX2/ssim_avx2.c

Source/Lib/Encoder/Codec/EbCodingLoop.c

Source/Lib/Encoder/Codec/EbEncDecProcess.c

Source/Lib/Encoder/Codec/EbFullLoop.c

Source/Lib/Encoder/Codec/EbFullLoop.h

Source/Lib/Encoder/Codec/EbModeDecision.c

Source/Lib/Encoder/Codec/EbModeDecision.h

Source/Lib/Encoder/Codec/EbModeDecisionProcess.c

Source/Lib/Encoder/Codec/EbModeDecisionProcess.h

Source/Lib/Encoder/Codec/EbPictureControlSet.c

Source/Lib/Encoder/Codec/EbPictureControlSet.h

Source/Lib/Encoder/Codec/EbProductCodingLoop.c

Source/Lib/Encoder/Codec/EbRateControlProcess.c

Source/Lib/Encoder/Codec/EbRateDistortionCost.c