Ability to pass location codes in CSV format

[ZeidH]

For both the CLI and Exporter you can now pass a comma-separated list with the --location param or the GRID_INTENSITY_LOCATION environment variable.

The response format remains unchanged as it already returned a JSON array.

[rossf7]

@ZeidH Thank you!

From a Go POV this LGTM however it would be good to update the help text now that multiple locations are supported.

We use the cobra library for this and the flag is on both the root and exporter commands so ideally it should be a constant.

grid-intensity-go/cmd/root.go

Line 61 in 24d2781

rootCmd.Flags().StringP(locationKey, "l", "", "Location code for provider")

grid-intensity-go/cmd/exporter.go

Line 29 in 24d2781

exporterCmd.Flags().StringP(locationKey, "l", "", "Location code for provider")

Are you OK to add that?

[rossf7]

LGTM