Add influenza data to hhs_hosp

[krivard]

We now surface HHS's influenza-related hospital admissions in Epidata:covid_hosp. To make these figures easier to access for researchers, we should include them in Epidata:covidcast:hhs as well so that they can be pulled using the covidcast libraries.

The following columns are available:

• icu_patients_confirmed_influenza
• previous_day_admission_influenza_confirmed
• previous_day_deaths_covid_and_influenza
• previous_day_deaths_influenza
• total_patients_hospitalized_confirmed_influenza
• total_patients_hospitalized_confirmed_influenza_covid

plus coverage variants for each.

We probably want previous_day_admission_influenza_confirmed. Are there any others we should add?

[krivard]

cc @elray1, do you need anything other than previous_day_admission_influenza_confirmed for your work?

[elray1]

Thanks, @krivard -- nope, just that column will be sufficient for our needs!