On attempted downgrade, we need to check each time-series collection and ensure that 'bucketMaxSpanSeconds' and 'bucketRoundingSeconds' correspond to a valid 'granularity' setting, and refuse to perform the downgrade if not.

Additionally, we need to ensure that 'granularity' is set to the appropriate value, and remove 'bucketRoundingSeconds' from the options in order to proceed with the downgrade.