Update createMetadata

[FrancescaMancini]

Add code that identifies the most recent run when most_recent would be true for an "exception"

[DylanCarbone]

For context, this is from issue #90 :

We need to add a list (called exceptions.csv) to the object store to allow createMetadata to identify those model runs that should not be used for indicator production (for now only those that include LERC data). This list needs to be updated every time we add outputs and data to the object store that should not be used in other projects.