add dataset with estimated NHSN hospitalizations for unreported weeks

[vpnagraj]

NHSN flu hospitalization reporting was paused in April 2024. it is set to resume in November 2024. we do not expect data for the intervening weeks to be reported. such a large gap will create changes with downstream modeling and plausibility analysis. we have begun looking into methods for imputing this data. we should include the estimated data as a exported data.

[vpnagraj]

this was related (nearly a duplicate?) to #227 , which was closed after #228 was merged in.

closing for now.