New constituentMultiplier field in API endpoint

To allow for index components that represent a non-unit amount of the base currency (for example tokenized stocks which might represent 2 or more of the underlying stocks each after accounting for reinvested dividends and stock splits), we will be adding a constituentMultiplier field to each record in the `instrument/compositeIndex` API endpoint. There will be one record for each record representing a constituent of the index, and it may vary over time. There will not be a record for the BMI index aggregated records. In the meantime, if you have any questions, please contact support.