Deploy COVIDnet source and signal

[krivard]

We have a prototype COVIDnet indicator in main, but it hasn't been deployed yet due to low state coverage. COVIDnet source data is available more broadly at the HHS level, but the API doesn't support HHS yet. To deploy this signal, we need to:

• Fix Consider adding COVIDcast support for HHS regions delphi-epidata#192: API acquisition support for HHS regions
• Add HHS handling to the COVIDnet indicator
• Determine if it's appropriate to convert the COVIDnet indicator to use the geocoding utilities in the delphi_utils package. If so, do so.