docs: Clarify the `manage_master_user_password_rotation` functionality #364

Job	Run time
Collect workflow inputs	5s
Max TF pre-commit	1m 35s
Min TF pre-commit (.)	26s
Min TF pre-commit (./modules/db_instance)	25s
Min TF pre-commit (./modules/db_option_group)	24s
Min TF pre-commit (./modules/db_parameter_group)	20s
Min TF pre-commit (./modules/db_instance_role_association)	20s
Min TF pre-commit (./modules/db_subnet_group)	25s
Min TF pre-commit (./modules/db_instance_automated_backups_replication)	24s
Min TF pre-commit (./examples/replica-mysql)	24s
Min TF pre-commit (./examples/role-association-postgres)	26s
Min TF pre-commit (./examples/complete-postgres)	25s
Min TF pre-commit (./examples/groups)	22s
Min TF pre-commit (./examples/enhanced-monitoring)	26s
Min TF pre-commit (./examples/complete-mssql)	28s
Min TF pre-commit (./examples/s3-import-mysql)	23s
Min TF pre-commit (./examples/replica-postgres)	24s
Min TF pre-commit (./examples/complete-mysql)	23s
Min TF pre-commit (./examples/blue-green-deployment)	21s
Min TF pre-commit (./examples/complete-oracle)	27s
Min TF pre-commit (./examples/cross-region-replica-postgres)	30s
	9m 23s

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