feat: making kine container image configurable via kamaji flag

A new CLI flag (`--kine-container`) has been introduced, with the
default value of `rancher/kine:v0.9.2-amd64`. It can be overridden also
using the kamaji configuration file (`kamaji.yaml`) using the key
`kine-image`.

main.go

@@ -76,6 +76,7 @@ func main() {
 			KineMySQLSecretNamespace:  conf.GetString("kine-mysql-secret-namespace"),
 			KineMySQLHost:             conf.GetString("kine-mysql-host"),
 			KineMySQLPort:             conf.GetInt("kine-mysql-port"),
+			KineContainerImage:        conf.GetString("kine-image"),
 		},
 	}