Internal
Add a dataflow-specific default frequency when the caller omitted one, and normalise the legacy freq alias to the SDMX 3.0 FREQUENCY dimension name.
freq
FREQUENCY
IMF dataflow identifier used to look up the default frequency.
Caller-supplied dimension filter map (may include freq or FREQUENCY).
Normalised filter map with FREQUENCY populated if it was absent.
Add a dataflow-specific default frequency when the caller omitted one, and normalise the legacy
freqalias to the SDMX 3.0FREQUENCYdimension name.