cmd/catalog: Default to the $KUBECONFIG environment variable (#2303)

Update the catalog operator and default to the $KUBECONFIG environment
variable value when the --kubeconfig flag hasn't been provided. This
mirrors the same way that the olm operator (e.g. controller-runtime is
handling this check under-the-hood) behaves.

Signed-off-by: timflannagan <timflannagan@gmail.com>

cmd/catalog/main.go

@@ -38,7 +38,7 @@ const (
 // config flags defined globally so that they appear on the test binary as well
 var (
 	kubeConfigPath = flag.String(
-		"kubeconfig", "", "absolute path to the kubeconfig file")
+		"kubeconfig", os.Getenv("KUBECONFIG"), "absolute path to the kubeconfig file")
 
 	wakeupInterval = flag.Duration(
 		"interval", defaultWakeupInterval, "wakeup interval")