Add flu hospitalizations to hhs_hosp

[krivard]

Description

Adds influenza hospitalizations as a new set of signals in the hhs_hosp pipeline for the hhs source.

Changelog

Itemize code/test/documentation changes and files added/removed.

• constants.py: add new signal names
• run.py: configure column mapping for new signal names
• test_run.py: add columns to source and expected for new signals
• test_response.json: replace with new raw epidata output (only used for counting number of files exported so the contents don't matter)

Fixes

• Fixes Add influenza data to hhs_hosp #1338