feat: add ability for users to specify alternative kubeconfig and kubecontext

This will provide the possibility for users to talk to existing kubernetes clusters, thereby removing one of the biggest reasons for having the old scheduler-kubernetes plugin around.

plugins/scheduler-k3s/functions.go

@@ -1142,12 +1142,25 @@ func installHelm(ctx context.Context) error {
 	return nil
 }
 
+func isKubernetesAvailable() error {
+	client, err := NewKubernetesClient()
+	if err != nil {
+		return fmt.Errorf("Error creating kubernetes client: %w", err)
+	}
+
+	if err := client.Ping(); err != nil {
+		return fmt.Errorf("Error pinging kubernetes: %w", err)
+	}
+
+	return nil
+}
+
 func isK3sInstalled() error {
 	if !common.FileExists("/usr/local/bin/k3s") {
 		return fmt.Errorf("k3s binary is not available")
 	}
 
-	if !common.FileExists(KubeConfigPath) {
+	if !common.FileExists(getKubeconfigPath()) {
 		return fmt.Errorf("k3s kubeconfig is not available")
 	}