fix: use image pull secrets instead of registries.yaml to reference private repositories

While this will now more or less require a local docker login - which can be overridden by setting the image-pull-secrets property - this ensures every deploy has a valid context.

One annoying thing is that the secret is per-app vs global, meaning that if the secret must be rotated, all apps need to be redeployed. A future change can fix that by deploying a global secret, or if folks really desire, this can be done by setting the image-pull-secrets property on the app/globally.

plugins/scheduler-k3s/functions.go

@@ -1120,10 +1120,6 @@ func isK3sInstalled() error {
 		return fmt.Errorf("k3s binary is not available")
 	}
 
-	if !common.FileExists(RegistryConfigPath) {
-		return fmt.Errorf("k3s registry config is not available")
-	}
-
 	if !common.FileExists(KubeConfigPath) {
 		return fmt.Errorf("k3s kubeconfig is not available")
 	}