Endpoints should support wildcard "*" for `geo_values`

[nmdefries]

• All endpoints should accept wildcard for geo_values
• All endpoints should use wildcard by default for geo_values

The difficulty with this is that we don't know allowed geos for any (non-covidcast) endpoints. The server side doesn't check geo validity either. We should figure out included geos as part of endpoint documentation upgrades, which will let us explicitly list allowed geos for each endpoint and check user input against that.

[nmdefries]

This could cause some requests to hit the row limit. Does that need special handling?