Add Why TimeGPT notebook #1340

Job	Run time
check-import (3.9)	8s
check-import (3.9)	8s
check-import (3.9)	8s
run-local-tests (macos-13, 3.9)	9m 17s
run-local-tests (macos-13, 3.9)	7m 0s
run-local-tests (macos-13, 3.9)	8m 48s
run-all-tests (3.9)	10m 10s
run-all-tests (3.9)	10m 10s
run-all-tests (3.9)	9m 9s
check-import (3.10)	11s
check-import (3.10)	11s
check-import (3.10)	11s
run-all-tests (3.10)	8m 13s
run-all-tests (3.10)	8m 13s
run-all-tests (3.10)	9m 6s
run-local-tests (macos-13, 3.10)	8m 1s
run-local-tests (macos-13, 3.10)	8m 1s
run-local-tests (macos-13, 3.10)	12m 0s
run-local-tests (windows-latest, 3.9)	11m 20s
run-local-tests (windows-latest, 3.9)	11m 20s
run-local-tests (windows-latest, 3.9)	10m 45s
run-local-tests (windows-latest, 3.10)	11m 35s
run-local-tests (windows-latest, 3.10)	11m 35s
run-local-tests (windows-latest, 3.10)	12m 23s
	2h 58m 3s

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