check_duplicates: Check that there are no duplicate forecasts
Description
Runs get_duplicate_forecasts() and returns a message if an issue is
encountered
Usage
check_duplicates(data)
Value
Returns TRUE if the check was successful and a string with an
error message otherwise.
Arguments
data
A data.frame (or similar) with predicted and observed values.
See the "Target format" section in Details for additional information
on the required input format.