Add Why TimeGPT notebook #1358

Job	Run time
run-all-tests (3.9)	15m 30s
run-all-tests (3.9)	12m 54s
run-all-tests (3.9)	12m 54s
check-import (3.9)	8s
check-import (3.9)	8s
check-import (3.9)	8s
run-local-tests (macos-13, 3.9)	41m 6s
run-local-tests (macos-13, 3.9)	1h 0m 12s
run-local-tests (macos-13, 3.9)	59m 23s
run-local-tests (macos-13, 3.10)	41m 6s
run-local-tests (macos-13, 3.10)	1h 0m 13s
run-local-tests (macos-13, 3.10)	1h 0m 14s
run-local-tests (windows-latest, 3.9)	10m 44s
run-local-tests (windows-latest, 3.9)	10m 44s
run-local-tests (windows-latest, 3.9)	10m 44s
check-import (3.10)	10s
check-import (3.10)	10s
check-import (3.10)	10s
run-all-tests (3.10)	14m 59s
run-all-tests (3.10)	14m 59s
run-all-tests (3.10)	14m 59s
run-local-tests (windows-latest, 3.10)	11m 37s
run-local-tests (windows-latest, 3.10)	11m 37s
run-local-tests (windows-latest, 3.10)	11m 37s
	7h 56m 26s

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