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/scheduler_k3s.go

@@ -29,6 +29,8 @@ var (
 		"deploy-timeout":         true,
 		"image-pull-secrets":     true,
 		"ingress-class":          true,
+		"kube-context":           true,
+		"kubeconfig-path":        true,
 		"letsencrypt-server":     true,
 		"letsencrypt-email-prod": true,
 		"letsencrypt-email-stag": true,
@@ -42,6 +44,7 @@ var (
 const DefaultIngressClass = "traefik"
 const GlobalProcessType = "--global"
 const KubeConfigPath = "/etc/rancher/k3s/k3s.yaml"
+const DefaultKubeContext = ""
 
 var (
 	runtimeScheme  = runtime.NewScheme()