Add insecureSkipVerify option

[helenosheaa]

if the flightsql server requires a certificate we should provide the user the option to switch off verification of the certificate by disabling that the client verifies the server's certificate chain and host name using the using tls.InsecureSkipVerify = true

as in this example https://github.com/voltrondata/flight-sql-server-example we need certs that we don't currently support

we might want to consider similar configuration as the MySQL datasource plugin, https://github.com/grafana/grafana/blob/2578774188e3cd89b5387563e0932c84ad834e75/public/app/plugins/datasource/mysql/configuration/ConfigurationEditor.tsx#L115-L167

[TaoVonQi]

Thank you for raising this issue. I'm trying to use the above example and this is what is currently blocking me.