EulerDiscreteScheduler add `rescale_betas_zero_snr` #776

Job	Run time
Setup PR Tests	2m 49s
Hub tests for models, schedulers, and pipelines	1m 52s
Run PR Tests (models)	1m 49s
Run PR Tests (others)	1m 40s
Run PR Tests (schedulers)	2m 5s
Run PR Tests (core_pipelines)	9m 28s
Run PR Tests (pipelines)	4m 58s
	24m 41s

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