docs: Clarify the `manage_master_user_password_rotation` functionality #282

Job	Run time
Collect workflow inputs	7s
Max TF pre-commit	47s
Min TF pre-commit (.)	22s
Min TF pre-commit (./examples/autoscaling)	21s
Min TF pre-commit (./examples/s3-import)	24s
Min TF pre-commit (./examples/multi-az)	21s
Min TF pre-commit (./examples/serverless)	23s
Min TF pre-commit (./examples/postgresql)	26s
Min TF pre-commit (./examples/mysql)	21s
Min TF pre-commit (./examples/global-cluster)	23s
	3m 55s

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