add optional `providers` flag to `countries list` command

[majesticio]

pass a providers ID to --providers to fetch a list of countries with that providers ID available. eg: openaq countries list --providers 119 to fetch a list of countries with airnow data

[russbiggs]

Is this currently implemented in the API? I' get a 500 when trying to pass a parameters_id= in the query string

[majesticio]

looks like right now we are just counting the providers for the countries resource eg: "providersCount": 4

[russbiggs]

no longer adding these query params