Add `window_function` attribute to `TimeDimensionSpec` #4540

Job	Run time
MetricFlow Packages Tests (3.9)	3m 28s
MetricFlow Tests (PostgreSQL)	2m 28s
MetricFlow Packages Tests (3.12)	3m 23s
MetricFlow Tests (DuckDB) (3.9)	3m 0s
MetricFlow Tests (DuckDB) (3.12)	2m 52s
MetricFlow Unit Tests	1s
	15m 12s

Provide feedback