Use custom stable repo for helm 2 client-only (kanisterio#878)

Before actually packaging the helm chart, we run
```
helm init --client-only
```
this command actually tried to update stale stable
helm repo. Which has been deprecated, we are adding
custom stable repo to get around that problem.

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

build/release_helm.sh

@@ -56,7 +56,7 @@ release_helm_charts() {
 main() {
     version=${1:?"chart version not specified"}
 
-    helm init --client-only
+    helm init --client-only --stable-repo-url https://charts.helm.sh/stable
 
     helm repo add kanister ${HELM_RELEASE_REPO_URL}
     release_helm_charts helm/profile "${version}"