Treat position bias via GAM in LambdaMART #6986

Job	Run time
r-package (ubuntu-latest, gcc, R 3.6, cmake)	12m 23s
r-package (ubuntu-latest, gcc, R 4.2, cmake)	14m 3s
r-package (ubuntu-latest, clang, R 3.6, cmake)	16m 10s
r-package (ubuntu-latest, clang, R 4.2, cmake)	13m 32s
r-package (macOS-latest, gcc, R 4.2, cmake)	14m 59s
r-package (macOS-latest, clang, R 4.2, cmake)	18m 1s
r-package (windows-latest, MINGW, R 3.6, cmake)	15m 54s
r-package (windows-latest, MINGW, R 4.2, cmake)	15m 27s
r-package (windows-2019, MSVC, R 3.6, cmake)	12m 3s
r-package (windows-2022, MSVC, R 4.2, cmake)	12m 37s
r-package (windows-latest, MINGW, R 3.6, cran)	26m 58s
r-package (windows-latest, MINGW, R 4.2, cran)	17m 8s
r-package (ubuntu-latest, gcc, R 4.2, cran)	20m 2s
r-package (macOS-latest, clang, R 4.2, cran)	27m 10s
r-rchk (ubuntu-latest, gcc, R 4.2, cran)	14m 43s
r-package (debian, R-devel, clang)	15m 36s
r-sanitizers (ubuntu-latest, R-devel, gcc ASAN/UBSAN)	19m 19s
r-sanitizers (ubuntu-latest, R-devel, clang ASAN/UBSAN)	45m 17s
all-r-package-jobs-successful	2s
	5h 31m 24s

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