`covidcast` endpoint - inconsistent handling of ISO format dates

[dshemetov]

A list of ISO-format dates is ok:
https://delphi.cmu.edu/epidata//covidcast/?data_source=hhs&signals=confirmed_admissions_influenza_1d_prop_7dav&time_type=day&geo_type=state&time_values=2021-01-01,2021-01-02&geo_values=ca

But a range is not:
https://delphi.cmu.edu/epidata//covidcast/?data_source=hhs&signals=confirmed_admissions_influenza_1d_prop_7dav&time_type=day&geo_type=state&time_values=2021-01-01-2021-01-02&geo_values=ca

[krivard]

The ISO format for ranges is YYYY-MM-DD--YYYY-MM-DD (two dashes) which in theory we should accept but it looks like that is also not working, e.g.

https://delphi.cmu.edu/epidata//covidcast/?data_source=hhs&signals=confirmed_admissions_influenza_1d_prop_7dav&time_type=day&geo_type=state&time_values=2021-01-02--2021-01-02&geo_values=ca

vs

https://delphi.cmu.edu/epidata//covidcast/?data_source=hhs&signals=confirmed_admissions_influenza_1d_prop_7dav&time_type=day&geo_type=state&time_values=20210102-20210102&geo_values=ca

• We should return an error message if someone attempts an ISO range with only one dash
• We should handle ISO ranges the same way as YYYYMMDD ranges

[melange396]

The ISO format for ranges is YYYY-MM-DD--YYYY-MM-DD (two dashes) which in theory we should accept

Indeed, this is supposed to handle that ISO range format, but is either malfunctioning or is not in the processing chain for the time_values argument on that endpoint.

[dmytrotsko]

PR with fix